If you keep this person on the payroll. That sends a message to your staff that you condone it.

No. You can keep someone on payroll and be clear about wha's acceptable behavior in the workplace or not. Don't conflate paying someone with condoning their behaviour. That bullshit shifts behaviour onto the shoulders of the business owner as opposed to who it actually belongs to; the person who's carrying out those actions. OP can try and influence the behavior it in the extreme, remove the person from the company, but that employees personal actions are NOT automatically condoned just because they're on payroll.

But if it becomes a problem with repeatedly asking then that’s a concern.

OP was clear they were asked a series of questions, once. They heard that there may have been other incidents.

You can ask for someone’s number and say they’re pretty.

What you "can" or "can't" do is actually a contract between you and the people you interact with; I'm not sure why you think you know what's okay for these people.

That should be taken as a compliment, even from a homeless guy.

What the hell is wrong with you? Some people would take it as a compliment, others not. That's up to them, not you. Also, the other party being homeless or not is completely irrelevant, and very dehumanizing of you to even make that distinction. You seem to think homeless guys are less than human. Disgusting.

But if it keeps happening it’s an issue.

No. If it keeps happening after they've asked for it to stop, then it's an issue.

IMO these comments are really destructive or at least unhelpful.