I have been on one biologic or another since early 2006. I do not get infections any more than I used to. Actually, I am sick LESS often than I used to be.
If I cut myself, it does not get infected any more than when I was not on biologics. I have had surgery, heart ablation, and my regular scopes without any issues. I work in the yard, get dirt under my nails, and bit by bugs. I shake hands with people, travel, camp, swim, and boat. I use public transit. I do all these things without wrapping myself in plastic or wearing gloves.
But, I get my flu shot religiously every year, and make sure everyone in my household does too. I do not get up close and personal with people I know have a contagious illness. I wash my hands often and try not to touch my face when I am out touching contaminated surfaces (basically most of the world). If I would remember to bring it, I probably would use hand sanitizers when out and about. But, I have gotten out of that habit.
Once you have been on it a few months, the anxiety should wear off a bit. Try not to let this make you nuts, because it can. I am not sure that homeless people would be any more of a threat than anything else, unless it is a group of homeless people with active TB. It is mostly a common sense thing, not as if your immune system becomes totally wiped out.
Good luck!
Jan