Okay, I'm not 100% certain, but I'll safely assume the Karsite has a LA+2.
Also, you're starting at level 8. Okay.
This is all according to the LA reduction rules from UA.
First, you get ALL the Karsite abilities. That's just how it works. If you want to work with your DM for a scaling ability/template class that's cool, but normally you just get everything at once.
Now your ECL is 10. Your class levels are 8, which is 3x your LA or more. So you can reduce the LA to +1 instead of +2.
You pay your ECL-1 (9) x 1,000 XP. So you need to pay 9,000 XP, when you have it.
Repeat the process at 11th level (ECL 12-1 = 11,000XP).
As you currently stand, you are ECL 10 with the experience of an ECL 8 character. Thus, until you have enough XP to get you to level 11, you won't level. Once you have 9,000XP you can spend it and lower yourself to ECL 9 (and then, when you get enough XP to level to 10, you'll level again). By that time your party will likely have gotten to ECL 9 (since you were 2 ECLs above them, you gained less XP). And you should be able to catch up quickly.