First combat in The Lost City is imminent. This is a challenge for me and the players and is in the nature of a shake down cruise. They get to find out how all their powers work, I get to find out how the monsters work and what will challenge them (or not, as is so often the case). At the end of this fight, they all get the opportunity to do some rebuilding based on experience. With the plethora of powers and feats now available, it's fatally easy to pick something that doesn't work the way you hoped. It seems only fair to allow that to change at the outset, given that leveling in PbP is slow.
So is combat. That can't be helped, but I try to move things along as fast as I sensibly can without out-running the players. In practical terms this means a 24 hour spot in which to post after any given player's turn comes up. Then (in theory, at least), I either delay or act on their behalf.
One suggested way around this is to turn all the players loose and let them roll and narrate their actions at will. This simply does not work under 4e rules when so many of the powers are interactive and dependent on what everyone else is doing. By the time someone has taken their immediate interrupt three moves after the trigger occurred, you may well end up reconstructing the entire encounter. Frustrating for everyone. One at a time then, so I can update the map and narrate between turns. It is labour intensive, but much less so than endlessly backtracking.
On the subject of leveling up - I award either double or 50% over normal XP budget which normally works out at about 5 encounters per level. Half the recommended number for a table game, but still taking around 3-6 months. It's the best compromise I've come up with so far, but the system continues to be tinkered with all the time.
Meanwhile, the map is ready and monsters await. It's like having stagefright every single time.