I fairly sure* it's extra spells every two levels (but at odd PM levels - 1, 3, 5, etc).[size=-3]*I qualify this guess with an admission that I am often wrong.[/size]
It's possible to get things "taken back," though it's an arduous process on both your end and the Team's. Moreover, the CDQ(s) you'll be doing to become a palemaster are part of your character's story. If you do all that, then decide the mechanical benefits of palemaster aren't up to par, it's like you just tossed out that part of your character's life, that part of his/her story. Not to mention the hours wasted on something you decide not to pursue because it didn't give you the mechanical benefit you were after. Still, it's good you ask now, so you can be sure that it's the route you want to take.In general, if you're taking the class more for the mechanical (out-of-character) benefits than for the character/social/political (in-character) benefits, then I'd suggest reconsidering taking the class at all. Obviously, we take classes for their mechanical benefits; it's just that the mechanical benefit of the class should be subject to character and story development.Also, I've updated the [LORE]Pale Master[/LORE] page to reflect the questions you brought up.
Well, there are atleast two PMs that I know of...
We did have a Palemaster on the server who retired the character for his own reasons... I think the character was at retirement a total of level 20ish and had a pretty deep and rich persona. I know one of my characters cursed the ground he walked on and she pretty much likes every one. If you're worried about the mechanics, then do a test build in a NWN leveling module, the Vault has a few to chose from. Re-builds are rare and must have a significant role play reason to be done.
As to the original post, you get new spell slots every odd level.
Every 2 levels, the pale master gains additional spell slots per day, as if she had leveled in her previous spell caster class. This gain only applies to spells per day - not caster level - and it does not grant additional spell slots past the usual maximum at level 20.
Warning: the pale master's caster level only increases by 1 every 2 levels, so a level 10 wizard/ level 30 pale master would have caster level 25 (10 + 30/2), compared to caster level 40 for a level 40 wizard. This is sometimes a considerable disadvantage.