Cool, and good to know - GMing pbp is a very different experience but not a hard one. Actually, I often enjoy it more since you never feel so on the spot. Keeping the pacing right - with the game moving forward steadily, but not leaving anyone behind - is the trickiest bit. My best bit of advice is to keep communication open in OOC.
I've been hunting a new job for the last few weeks, so expect me to be on...well, quite a lot. Once I get something new, I'll probably still be on daily but I usually like to give myself a bit of time to percolate a response, so every couple days is typical unless I'm in the flow.
Combat can seriously drag, yes. My preference in stuff like this is pretty much what you stated: we post our intentions, you sort it out, each round taking no more than 2-3 days, including any back and forth (saving throws, attacks of opportunity, that sort of stuff can grind everything to a halt). Ultimately, please feel free to make any rolls for me, just post the formula so I can pipe up if you missed a stat or ability.
As for starting the adventure, yes, basic "arriving and settling in" sorts of posts will take a few days by themselves. It sort of depends when you want things to kick off.