This is large post so might as well grab a popcorn and make yourself comfortable.
Before you delve further into the post, I would like to make this clear that this is only my suggestion and has no other implications and meanings. You take it however want to but remember that these are just words on a website. No need to get angry or aggressive over this.
I'll also edit or reply to this if i get an Eureka effect on what else i could suggest to add.
There's alot to cover here so I'll make a Table here to for you to Ctrl + F to jump to certain parts:
2. Managing a city
4. Outposts and New Frontier
5. Stuff that i'll explore later
6. Closing ramble
After Finishing the game, Let's just assume you get to manage the city (Because that's probably the most logical thing after managing your mansion. And more content the better for the player and the Game and thus indirectly the dev ) I got these ideas from Total war Rome 2 but they don't have 1 to 1 import now do they? And in the game Managing your provinces, settlements, edicts, public order and all that jazz is like another game within the game. Which is why I thought they would fit in. Total war Rome 2 wasn't my only inspiration and I'll be citing where I got (plagiarized) the ideas.
2. Managing a city
This game at it's heart is management game with RPG elements. Now managing a City is going to be much more headache inducing than a single structure (Your mansion). But also much more rewarding for you. Here's a bit of overview of things that you'll be able to do.
Taxes and maintenance - As you become a Mayor? Owner? Emperor? of a settlement all of it's virtues and it's problems are yours.
City Development - Rome wasn't built overnight. So grab some hammer and nails.
Land Development and Resources - You didn't think you can just cram more people into ever more claustrophobia inducing space did you?
Public order - A basic numerical information on how chill or not the settlement is doing. Affects event generation and other aspects of the game.
Research and Development - You have to learn how to build before you do it.
Statecraft and Slaves - These things might be too much for single person. Might as well outsource it your "slaves".
Outposts and New frontiers - A Home away from Home.
2.1 Taxes and Maintenance.
As you gain possession over structures you'll be able reap it benefits and pay for it's expenses. For example the brothel in Wimborn will generate gold and help with Public order (Covered later) but will also Consume food (Covered later) and need "Workforce" (Covered later)
2.2 City Development.
So you have authority over buildings, good, now what? Let's make them better. That's gonna cost but it'll be worthwhile. Now there's a whole section for Research and Development (From now on Shortened to R&D) and how they'll affect this aspect of the... Mod? I guess? Building new structures to help with the city and in turn give you more gold are what's this is about. There's 2 aspects for this feature;
Creating and Developing. Let's take the Slavers' guild for example. It offers around 4-6 slaves of varying level and grade. Now you can upgrade that building to do more things like; Offer you more slaves for sale, Higher levels slaves, Lower price for slaves, Increase it's efficiency for specialization, Actually train unwilling criminals to be more submissive etc etc. This is the development aspect.
So what about that Creation part? If you have gold, resources (Covered later), Workforce (Covered later) you can have new buildings for other purposes. For example a Constabulary (A British word for Law enforcement covering a specific city) to keep the populace safe and hold public order or an Arena (As suggested by someone else in this thread I forgot about) to generate entertainment which means more public order, profit from ticket sales, training in controlled area etc etc. This is the Creation part.
But that's only the part of it. You may have wondered what the "Workforce" is and it's quite simple, basically people able to work for
you The city. How do you gain them? Population. More specifically working residents are the workforce (Idea from cities skylines and Simcity).
2.2.1 Economics and population
Residents are possible venue of income through Subsistence and taxes. But for that they actually need few things.
1. Place to live. (Remember the creation part? Start making some hovels mate)
2. Place to work. (This is where you get the Workforce from)
3. Place to spend their gold. (More taxes More gold)
This means there're 3 bases to cover. Residential area and buildings, Industrial area and buildings and lastly Commercial area and buildings. Each of them needs both Land to be built on (Covered later) and Resources to be spent. Here's a simple formula for how this works;
1. Build residential structures to attract residents.
2. Build workplace for them to work effectively turning them into a usable Resource.
3. Build commercial area (The market) for them to acquire you know things like food for their basic needs.
4. Residents pay you indirectly through subsistence and sale taxes.
Now that you have workforce you can assign them to work in certain things like
Erecting statue in your likeness to feed your ego Acquiring more basic resources through mining, foraging, lumbering to further upgrade buildings and give you back an actual useful stuff.
But wait how do you get food? From the commercial areas of course. But where do they get it? You have to make that. For example Wimborn has farmlands surrounding it that generate food. Get some land (Covered below) and start making food.
2.3 Statecraft and Slaves.
Although the word Statecraft looks intimidating this basically means (Defined by Google) the skillful management of state affairs. Buildings need to be managed, assign your trusted and capable slaves and they'll generate more gold along with whatever extra resource and bonuses that structure offers you. This is to alleviate the player from Micro-Managing everything. And once you Fully develop and assign slaves to the jobs, you can go back to living in luxury while the gold flows in. And you'll reap the benefits your new structures provide to you, your slaves or your city.
2.4 Land development and Resources
Now that you're reaching the limit of how much you can build in the Settlement, you have to expand it's area of influence. So in order to do that we have to drive some unnecessary elements out of our "Future land". Remember the bandits that always seem to go in pairs (even though they're sometimes in triplets)? Yeah those guys, we gotsa drive them away or even better, "assimilate" them into our society. Now they won't just stand and watch as you attempt to get rid of them. Most likely they'll band together in an attempt to resist you. This'll be much larger than your standard rabble you've come to known, Expect much larger and tougher group of them. Subjugate them and acquire more land for your city, so you can
Re-Establish T he third Reich turn it into something that you can use.
Now as much as you wish you could make building out of nothing but gold (as expensive and awesome as that may be) it's gonna be a No-No for now. So to build more buildings you need common building materials like lumber and stone. To acquire those you have to Develop your newly acquire land into a site that gathers raw materials. Lumberyard, Mineshaft, Hunters' lodge, Farmlands (No not the kind that you have. Actual farm that does agriculture.) etc etc. These are generators that create Resources which are needed for other stuff.
Don't wanna starve your
Slaves Citizens do you?
2.5 Public order
There's not too much about it.
Slaves Citizens have needs that has to be accommodated for. Look out for them by providing them with Food, Safety from criminals, Entertainment and everything will go well. Fail to do so and things will fall apart. Low public order causes the citizens to flee or rebel. (Idea from Total war Rome 2) Less citizens, less income, harder life. Rebellious ones might try to succeed you forcefully. You don't wanna get shanked in an alley do you?
2.5.1 Crime and Constabulary
Even in high public order some people just wanna see the world burn. Crimes like theft, harassment, robbery happens in everyday life. While you yourself and maybe along with 1 or 2 slaves are enough to squash this rabble but that's bit of a chore. Constabularies once built and fully manned make sure they think twice about harassing a Loli in a dark alley or become a obedient little slave in the market. Effectively generating more slave population (Easy work force for gold), and maintain public order from deteriorating by keeping the streets safe.
Now if you've played enough RPG and RTS games you should know that Tech trees and Skill trees are a thing. (Hopefully so I don't have to explain it) R&D is basically that but has a little bit to it. Managed by the Mage order (Before they became the government or another structure whatever floats your boat my dude). They actually have to do the Researching part of it. What I mean by that is, you have to send some people away to certain locations to gain insight about what's there to learn about it (Research). After that they can turn their research into something that can be used (Development). By having them study certain stuff from other settlements or from nature you can adopt their distinct advantages. Once developed you gain a new building, upgrade or the ability to further interact with certain stuff. How this'll work is that you can assign some slaves to develop your new technology each generating a resource which is basically the currency used to buy the research or a pseudo progress bar. Scaling with wit? and probably gnomes are better at this than me or you As an example.
4. Outposts and New Frontier.
Ever wanted to have nereids and scyllas just spawn in the Slave guild more often? Wished there was a settlement somewhere in the marsh, mountains or near the Ocean? If the previously stated features are implemented well, there's no reason not to create your own out on the middle of nowhere. Residents attracted are based on climate of the place. Near the ocean more nereids and scylla are attracted and become permanent residents given the opportunity. This also means possible crime and thus slaves of this race in the Local slave guild and more of that race circulating the global slave market (Lmao I never thought i'd type something like that). So there's something to gain from this. Though this also means each region will have their own specific ways of becoming self-sustaining and different technologies needed for this. (You're not gonna just plant seeds on the rocky terrain of the mountains)
5. Stuff that i'll explore later
Edicts (Resource drain that will give other bonuses)
Trade between Cities
Actual list of the tech tree and upgrades and list of common buildings
Legalize Marijuana Suggestion on how to implement Enchanting
6. Closing ramble
Well that was quite the odyssey and i could just keep going but things will become less and less thought out. Do tell me what else you'd like to see, Ask for clarification of what something you didn't get, etc etc. Also keep things civilized.