Homeless Sims aren't exactly homeless just so you know. It just means that where they live isn't "in town." These sims get all the rest they need unless you distract them all night and they eat just like everyone else in town. They'll visit the gym, the diner, the bistro or "go home". Sometimes these Sims will move into a vacant lot actually in town through story progression. These Sims are not to be pitied in any way. They just travel a little farther to come see you. In fact what you're calling a homeless Sim is basically a Sim that according to the paper "moved away from the hustle & bustle." If you want to make a community project, a fridge provides free meals like cereal and ice cream. Homeless Sims actually have money because most of them have jobs around town and that's why they're there to fill the voids that your game needs filling. These are the people that are your co-workers, your paparazzi, mixologists, bouncers, consignment clerks, register attendees, tattoo artists, etc. You see them in every game. The word homeless is only used because this means if you chose to marry one, you guys would have to stay in your house because you can't get to theirs.
As for Sims needing to potty, my brother in law is getting locally known for saying "everyone poops. they wrote a book about it."
Posted same time as Marian. She won!