You get to keep only enough to maintain a very modest lifestyle in a low-cost-of-living area, the rest of it has to go towards improving the world in some way.
Edit: Given the previous rules that you must maintain a very modest lifestyle in a low-cost-of-living area, would you rather choose to opt out and not have the money at all?
I wanted to do something similar to your apartment idea but for teens and young adults in poverty-stricken areas. Get them into a stable environment, teach them the necessary life skills like credit management, budgeting, cooking for yourself, etc. and give them job training. All of that would also go just as well for the homeless population. I grew up in an area that was riddled by the crack epidemic and had no resources for kids/teenagers to do anything other than crimes. The city didn’t pay for anything to keep us out of trouble, and our drug addict parents sure weren’t going to do it either. So I always felt like if I had a ton of money I would focus on program to help teens in those situations learn to be proper adults, because nobody else is teaching them. Schools won’t, parents won’t, we’re defunding every program that helps outside of the home. It’s a mess.
That sounds pretty good too, yeah. The program could be expanded to include safe spaces/training for teenagers and such too, probably include a rec center that always has stuff going on for them to participate in, etc. At that point it turns from a housing/job training project to basically a community, built around safe spaces, opportunities, and education for the future.