I will go through your categories first.

- Basics -

The way you want to focus on the 'treating people' and 'being a doctor in a hospital' from a gameplay standpoint, I would not add the 'Simulation' to the genre.

When adding the Simulation genre, people normally assume that the game will focus on a detailed gameplay experience, not just the thematic and objectives. Based on your description, it seems more like a game with the hospital tasks as its set-dressing.

- Premise -

It would certainly work, as a lot of games have come out like that before. (That being first person games with task solving / item handling and solving a mystery).

That being said, especially because of the point above, it is more a question of how well the game is executed to make for a round and polished experience.

Part of this is also the premise itself. While a lot of games would take what you wrote and be like 'Good enough to play', it would be good to focus on some more details. (Which you probably will anyway as this is just a rough concept).

For example: Is it believable that a doctor is sent as investigator, if they never worked in some sort of investigative environment? Based on how you described it, it would make more sense for me that the person they would hire would be a reporter or detective. But that of course would go against your gameplay routine.

So is it not working? Of course it is, you just have to work on the details (and not leave them out as a lot of people do), so to make this story in specific believable. This also heavily depends on the atmosphere and story points you are building, and how you are presenting them.

- System -

Most of these features seem very simple. Which is not the problem - but again stems into the question of 'How do you implement it'.

You can make work of very simple systems if you think through them and present them in a nice fashion to make them serve what they are supposed to.

That being said, every game should have some sort of 'big feature' which lets it stand out. If it is not in the story or atmosphere to make for an enjoyable experience fully on its own, there should be some sort of system mechanic that makes the experience memorable.

From your list I believe you want to focus strongly on the 'open' nature of the story's flow and how you can affect it. Which sounds good. But again, it needs to be implemented well to not confuse players. The player should have enough time to do, decide and look up things in order to get things right. The game also should give feedback to this accordingly to make it impactful. The way you want to divide the endings and add multiple playthroughs is a good factor to this.

A special note about the Side Quests: While I like the concept, you must make sure that it does not deviate too much from the rest of the game. It can work if you leave the player enough room to work with, and if it actually has a point in the overall experience. If it feels like unnecessary bloat while playing, players will probably skip it, meaning it does not make sense in the broader view. But this is something you must feel for yourself. Is it enjoyable, do you look forward to doing them? What is the reward: Additional or important items? Story input or flavour text? If it is the latter, is it done well enough to be interesting to players who care for it?

- Final thoughts -

This can definitely work, but as you figured out yourself: The game itself has not too strong of a gameplay focus in terms of 'Look, this is some crazy in-depth thing you can do, this is why you want to play the game!". It is basically a game with an interesting setting and mechanics that support the story, genre and experience.

Which of course means that these things have to be good. And that leads us to the final question of: How do you want to implement them?

Because there are several ways to do them and it comes down do getting the hang of it yourself, which is the most difficult part.

A game like this could work with a more underlying narrative but an excellent gameplay flow. Or it could set the story in great focus with telling and characters, putting the gameplay a layer down. Whichever you give more focus, needs to be better implemented. For the latter this of course means quite more ressources in a 3D game however. If you do not have them, I would consider the focus on an underlying story the player can figure out themself, making the gameplay flow most entertaining and atmospheric for them to go through.

A final thing to consider: They way you want to put the game flow together within one working day could work, but an alternative would be to make it into a 'Day Routine' and 'Night Investigation'.  Both come with their advantage and disadvantage in terms of development and experience. The latter would for example make it possible to divide tasks and the flow to make it not overflow during the day - if that would become the case. Putting it into one routine could also just be the thing to make it good, though. ... I wanted to get onto something here. Ah, right: The divide may or may not make it easier to lay out the story if you feel it does not work when putting all into one routine. So basically the same what I wrote above: Two presentations, depending on what you feel makes the game a better and more rounded experience.

I think that the key to making a game like this work is to have very engaging characters. With such a dialogue heavy medium, you need to make players want to put in the effort to interact with npcs. (I would recommend character creation as a main, early focus) If you look at something like Disco Elysium, the gameplay is simple but people adore it because the dialogue is written extremely well. 

As for the premise itself, I think that it seems interesting. I'll look forward to seeing how this develops.

I like your concept. This type of game is quite popular with casual game players if you use amazing graphics.

For example, Snark Busters is a detective story  where the player essentially wonders around and clicks things and has high-quality graphics.  

If you're making a full-length game - 8+ hours of game play - then I would recommend you don't start with this game because  it could take you months to complete if you're doing everything yourself and learning along the way.

Perhaps if you start by writing a few short games to learn about Unity and gaming. An idea would be to take the puzzle elements you want to put into the main game and write a short puzzle game with those elements. That way, when you start on the big project, you already know how to program most of it and whether you like game development and Unity.