"I am entirely incapable or many of the things mentioned" "I might be very good at coming up with certain types of examples or providing a certain kind of hard to articulate meta intuition. I also know a bunch abaut art and design." They've stated they're looking for people who can do just a one or a couple steps (as well as all-rounders), so sounds like you should go for it.

"I am unable to commit or fully participate due to helth and geographical reasons, and a bunch of other things... what should I do?" If I were you, I'd send in an email saying just that, but with more detail of course - what things you'd like to do, what limits on time you're likely to have etc. My guess is you'd still be a help, and if not you've only lost 5mins in checking.