Zaran
Adventurer
The last couple of fights (Especially the last) in Keep of the Shadowfell were extremely hard for the players that I ran this module with. You might not want to scale those up. The monsters and Kalarel by themselves aren't too bad but when you factor in the gate things get hectic especially if everyone is new to 4e. I would also make sure they take a short rest or if they feel they don't have the time, give them the benefits of a short rest before you do the fight with Kalarel.