Here's the thing, and I didn't come up with this, but:
If you've met one aspie....
You've met one aspie.
We're all very different people, after all, just like everyone else.
Do something with him you think both of you would enjoy.
Personally, I like a good conversation and maybe some liquid (with or without ethanol) and/or solid refreshment of some sort.
After that, well, that all depends on how it goes...
The only real guidelines are to just be honest and be yourself.
He's just a guy, after all, that you're friends with and seem to want to be romantic with.
If he's an aspie, he might be quirky in various ways, but he's mostly just a person, so treat him that way.
Welcome to WP! 