You should PM Turnsky about this. Though I dont know how frequent his comics come out. There are many webcomics that aren't released on a regular schedule. A good idea would also to be emailing authors of comics you like.
I'm fairly certain the story is laid out ahead of time, or else you run the risk of running out of ideas of going on an odd tangent that you cannot escape from... but I wouldn't know. Comics is too much for me at the moment.
1) how much time per week?.. it depends on what you want to put into it, for me, i can pull off.... four comics a week, possibly five if i push it, two comics per piece of paper, 10 hours between blank page, and photoshopped wonderment.
2) some have it scripted from the get-go, i do foxfire by the seat of my pants, as it were
3) a scanner, or drawing tablet (a mouse if you're devilishly good) and any photo editing proggy, Photoshop, the gimp, etc, etc.
4) generally anything that'll fit neatly in a webpage, i'd suggest veering very far away from
infinite canvas, but that's just my opinion.
5) one, two, twenty thousand, doesn't matter, as long as you have an update script running (comic genesis has one), you should be alright.
6) me?.. no, some have, some haven't, others, you can definitely tell that they haven't put pencil to paper before in their life.
7) it depends if you get stressed out easy, i don't, i actually enjoy making comics, and get jittery when i don't make a comic..
as edison said once, before you invent a lightbulb, one must figure out how NOT to make a lightbulb, and hence
http://hownottorunacomic.comicgenesis.com/