Don't worry about not having time to reply!
I usually just worry that my feedback is misconstrued to have bad intentions or something, since I often write a lot :D
For what you said about the customers and what to do with them, I recently played a brothel management game where you build rooms and hire women for them, then receive guests that have to be appointed to those rooms. It had an upgradeable male reception area, where you could also place staff as "distraction" if the q gets too long. Not fully sure right now what the best way to translate it into a profit/sec idler format would be, but a reception area with customers coming in, a receptionist greeting/delegating them and spicing the waiting line up with some buyable attractions could be nice.
Could even integrate a customer system into upgrades next to getting the girls (so you have one tree for buying things to make profit and one tree to improve customer base, like frequency/staying time/max waiting time etc), this way you could turn the gameplay into an input/output balancing act like "Finn Dorset's Institute For Livestock Replication". Although this would obviously be a massive undertaking and just something that came to mind.
Something else that could be nice would be something to click on or to do, even if it is only fun gimmicks and not directly connected into the gameplay loop. Most straight up example that comes to mind would be the closed window on the roof. If you could click on it, it opens and you see 2 people going at it for a couple seconds, then noticing it, being shocked and closing the window again would be a nice little gimmick that players could engage with. Also just kinda funny.
Aside from that the typography and formatting in the UI could use some work, but this is something that can evolve and improve over working on the game (like having text be centred optically within an element or better use of inner margins).