GM Doom, I just started my first PbP on this site (not first ever).
After I created a thread under Recruitment, the site gave me some options to set up a campaign. The thing I don't know how to do is close recruitment, but I'll make my own thread to ask that rather than hijack your thread.
Check out the Recruitment forum to see how others are attracting players.
I'm happy to offer any advice, though I'm afraid I don't have a proverbial seat at a table at the moment.
I think the big thing to remember is you're still putting in time when you GM PBP. The difference is it's not all in one chunk and you don't really have to worry about schedules as much. Instead, take those 3-4 hours and instead consider you'll likely need to devote 5-30 minutes a day (depending on level and action and other factors). The main thing, as has been noted elsewhere, is consistency and momentum. Good games get updated daily by GM and players and that builds off each other. Once one side stops doing that, the other side follows suit, and pretty soon the game is dead. You as GM have a little more responsibility in that regard, however: If one player takes 2-3 days to post every time while everyone else posts daily, you might need to bot that character, prod the player and/or consider replacing him/her (especially if that lack of posting holds up the action for the overall group).
The recruitment/application process is brutal on both sides. As a player, I've started PMing GMs running games that I enjoy reading, letting them know that I'd be interested to join if a spot opens up. As a PbP GM, I've had others do the same, and when I've lost players, I've filled those spots with either the original applicant pool, players who've expressed interest through PM, or players who I've enjoyed in other games and who've proven themselves to be committed and active.
Or else, start building some lvl 1 PCs and start looking for active recruitment threads that sound interesting to you. Or start reading threads and decide for yourself what works for you and what doesn't. Everyone's got a different style, but some conventions run across the boards. Check the sticky threads in this board for some very good advice.
If you haven't, read this post and this one.
I understand that this thread is always recruiting for PFS one-shots, which are a (relatively) quick way to get your feet wet. There was someone running a "PbP GMing 101" kind of course for prospective new GMs a while back, but I'm not sure if it's still on-going or if there are any openings.