This demo really tickles my brain. There isn't a lot to give feedback on, but I'm still going to.
I know this is a custom engine. Great work on that. The features that are implemented are responsive and work with no jank and no problems, which is already about 50% of the work of making it satisfying to play.
The demo needs an undo button. Even at this stage it's a must-have QOL feature.
A major problem a lot of these games have are the terrible artstyles. This style is great. It's a classic look but with a high-fidelity upgrade. It looks really really crisp.
Only major gripe is with the UI, since right now every tab button is on a single row, and I think they would be better off separated based on function, like in all the Tycoon games. Makes it more intuitive and easy to work with them.
I hope the UI isn't planned to ultimately keep this Sims 1 look because it makes it look unoriginal.
I want to play the game that eventually comes out of this prototype.