1/ Your First Erotic Scene 

An erotic games are mostly played for their erotic scenes so I think it's important to actually put as much work as you can on them. 

erotic scenes have the huge advantage of being easy to isolate from the rest of the game making it easy to create an erotic scene first and insert it into a gameplay loop created after. 

Being self contain and relatively short, erotic scene are perfect to create a template game around them. If it's for a visual novel, it allows you to preview how your game will look while if it is a more interactive game then you can already create gameplay loops around this erotic scene.

Starting with your erotic scene first also allow you to communicate easily (ex: on twitter/patreon) about your game providing erotic content for your audience at a very early stage of production and still be able to show something that your audience want in cases you decided to cancel this project after making the first prototype.

2/Preloading Assets

Even if your assets (Images/sounds/musics) are in your game folders, doesn't mean that your game will have direct access to them. 

You have to imagine that your game is a box on your desk. Everything that is on your desk can be immediately put inside the box to be played with, everything that is not on your desk has to be looked for. Each time you need something that is not your desk you will stand up and look for it in one of your named drawer. As you can see, it is a lot of action just to get one single asset and that's why not preloading assets will mostly create lags and bugs.  Especially because while looking for this specific assets things are still happening in your game box.

If you notice any type of lags just before a new assets is being called then it is probably a Preloading issue. Most modern engine have very clear way to preload assets but don't expect older engine to do it for you.  For example RPG Maker has no built-in way to preload assets so you'll have to do it either though plugins or manually.

Just so you know, Preloading will always be beneficial for your game but it is can be time consuming if you do it manually. If the asset is small enough, then your player will most likely not experienced any lag or issue. It is really only useful if you're trying to display big images, long music, have zero frame delays on your sound effects or if your game starts to crash/lag for no apparent reasons.

Here how to preload assets manually easily in any engine.