No different then anyone else you’d approach. When dealing with anyone with a disability we want to be typically treated as an equal. The same concerns and questions will probably come up as they would with anyone else. The worst otherwise is they may wish to have the final product described.

Do your absolute best to forget he's blind at all. The toughest part of social interactions is knowing that we are visibly disabled and being treated differently because of it. Don't overthink this any more than you would a normal conversation. Also, this sounds great; I know if it were me, I'd be more than happy with a description and a picture I could show to sighted friends. I'm sure it will be fine. Good luck!

Just like you’d approach anyone else to be a painting subject. He may be able to see your social medias himself, or get a sighted friend to verify for him, if he can’t. Or he may just be chill with it without checking…just like any other person.

If you explain that you’re asking how much he can see so that you can paint in a way he’ll also be able to see should help with that. It’s generally a bad idea to ask “how did you go blind?”, though as now you’re asking for detailed medical history, and that is pretty intrusive.

The only other thing I’d say is to explain that you want to paint him because he’s a local and distinctive enough to make a good painting subject , not because he’s blind. This will, of course, vary by person. But I sometimes get people telling me I’m amazing and inspirational because I’m doing a very mundane, easy task while blind. It’s weird, and tiring, and would personally make me wary of someone approaching me like this. But I’d feel better knowing you were painting various locals and not singling me out as so amazing walking through the park while blind.

Hey dude, I'm an artist and I want you to be a model for a project. Could I take some pictures of you walking around the park like you do everyday? I'll pay you 50 dolars for the inconvenience... You know the way, we're just common human beings. It doesn't hurt to ask, just don't be a weirdo.

Yeah just approach him like you would any other potential subject and ask. :) I’m sure he’ll be interested. Good luck!