First fandom in which I interacted (online and in person) with other fans: It would have been IRL (as there wasn't an online in those days; and I'm not sure, but I got involved with Doctor Who, Quantum Leap and Pet Shop Boys fandoms around the same time, the early '90s.
Pairing in the first (m/m) slash fanfiction I read: Pretty sure it was Sam/Al in some Quantum Leap fic.
First RPS/RPF I read: It was probably something in Mock the Week fandom, or possibly Have I Got News For You.
First fanfiction I read that made me think, YES, this is exactly the kind of fanfiction I'd like to write: I've never had that kind of epiphany; I've just always enjoyed using my imagination both to write original stuff and fanfic (even though I don't do it much).
Pairing in the first fanfiction I wrote: I don't often write pairings, but I sort of set out to write some slash once and came up with some Sam/Gene Life on Mars fic.
First OTP: Remus/Sirius (i.e. Harry Potter). There's a whole AU in my head in which they're living happily in a cottage in Gloucestershire and Harry occasionally visits them.
First RPS/F OTP: Russell Howard/Dara O'Braian.
First fannish friend I met in person: I started making penfriends in Pet Shop Boys fandom, and started meeting some of them in the early '90s at signings, Radio 1, etc. And then at a PSB fan event in 1991 I met Phil Newman, who's also part of Doctor Who fandom, and through him I started going to the Fitzroy Tavern. That was also around the time I went to a couple of one-day Quantum Leap cons.
First character I formally roleplayed: Despite enjoying roleplaying, I don't do it much, and definitely can't think of any known characters I've roleplayed.