Well, i have never modified a quest with KSE, i think the proble might come from that. See if you don't have an auto save, to roll back, and put the quest as before. When you have I have a bug like you with brook, i often try to reload the game, it's better if you have a savegame before entering the cave when vrook is already in.
Have you any other changes in your game, like mods etc?
For the rest, i have already do it and all worked fine, but sometimes when you change too many things the savegame is screwed up, so the better would be if you have an other save game, like an auto save, and make the changes one by one, to be sure that there isn't any problem, and if there is know which change is responsible. Often the probems are caused by the appearance, the items, and the feats/force powers.
the credits, i think there is a limit, wich no matter how much you put, it would be set at a limit.
And to have max evileness put it to 0 ^^
Entirely evil: 0=======50 neutral======>100 Entirely Good