Contact him on the basis of some common ground or interest (ideally one that might become something to do if/when you meet up with him). Or your family connection, that might actually be the better way. You don't have to express intentions yet, friendliness is just friendliness and it can stay that way. Trying to clarify what you have in mind at this point would probably be weird, just be cordial for now.
I guess it might depend on if you think you can sell it or not, but being generally unconcerned with if something might be seen as creepy can be a way from keeping it from actually being creepy. It's often easier to just do something and apologize afterwards than it is to ask for permission, and for this just contacting someone is not a big deal.
There's no guarantee he'll want to hang out, I mean you can already be an acquaintance with someone and have difficulty making that transition, so just view it as communicating that you'd be down with hanging out if he feels like it. If it's not really a big deal then no one will really perceive it that way, or at least not for long. I find that the vast majority of the time that I risk stepping over some possible boundaries, the other person just thinks I'm being nice or reaching out to them in some way.
And yes, I've been eating far too much ice cream and that's not a good thing by itself, lol. Summer will always be my least favourite season
