1) Simpler the better for the most part. You can always make your more complicated game later.
2) Make the game you want to make. The people who'll cry about you not catering to their fetishes weren't ever gonna give you any money anyway so fuck 'em.
3) Your actual workload is going to be at least twice as much as you think it is right now.
4) v0.1 is your foundation. If you're making a sandbox, make sure your variables are in check, because it's much harder to add things in later. You'll also want to make a good first impression as many have mentioned.
5) Be prepared for frustration. You're gonna have days where you're wondering why the fuck you do this. Days where you stare at the screen with no motivation. Days where you're trying to find that one bug that keeps messing with you. Days where people will literally go out of their way to say 'This game sucks' without elaborating. If you're crazy like most of us, you'll end up eager to chase the highs that come with game development anyway.
6) If you're making a sandbox game, for the love of God, if I can sum up simple actions with something as simple as 'you go through your morning routine', please do so. Nothing grinds my gears more than games where you have to click to wake up, then click to eat breakfast, then click to go to the bathroom in hopes your stepsister sees your magnum dong and is now deeply in love with you, and then click to go catch the bus, and then finally get on with your day.
As for recommendations:
Nothing is Forever is a great example of something that isn't visually amazing, but makes up for it in the writing. That game is one I constantly go back to due to how much more engaging the smut is due to the writing. Characters have clear motivations, kinks, and the scenes are a lot more than just 'Let's bang MC'. I also like the fact that it's probably the only game that can present reasons why the MC shouldn't pursue relationships whilst making them very tempting for both player and the character himself.
New Life isn't perfect, but it's a big influence on me as a developer. It's one of my favorite sandbox games as it gives you plenty of freedom without being overwhelming or overburdened with mundane tasks. Playthroughs can get a bit repetitive in the long run, but it's got some interesting elements that I feel can be built upon.
There are other games I like and could be recommended, but I'd say my best advice on that front is to find what you like, and see how you can spin it.