I've had a few zombies in here lately looking for jobs.
As to experience points. I won't try to tell you how to run your game, but I will share some thoughts I've been having lately. These thoughts have come about from my having been involved with dozens of games on both sides of the screen in recent years across 3rd, 3.5, 4th and pathfinder as well as a few more exotic systems.
First, the RAW (rules as written) don't seem to work in a way that I find satisfying for play by post games. As the Constables game passes the two year mark I find we are still significantly short of gaining two levels. This is disappointing to me as DM and so I can only imagine that it worse for the players.
What is the point of going up levels? The power of the characters changes relatively little given that we have lots and lots of foes and challenges available at any given CR. So the point of going up is not so much about power as options and a sense of accomplishment. Being able to do more cool stuff as you advance even if relative to the foes you face you really aren't more powerful. It is nice to have new toys and new powers. That's part of the fun. If you only go up a level every 13-15 months that fun is pretty spread out.
Levels become more important when you are running a published adventure as the challenges are already set. Such adventures are going to work better for the right strength of party.
I've been in a couple of games where the dm decides it is time for a new level, IG's game for example. At first I had my doubts. However, in practice it worked out well in these games.
Calculating exp., remembering to give it out and making sure totals are right is a pain in the ass.
The problems are the same in 4e and recently a game I'm in voted to go ahead and level up rather than wait. It seems to have worked out fine.
So I humbly suggest that you make the level break points fit where they should be for the adventure and don't worry about it otherwise. I shall do my best to roleplay at the current level or better.