Re: 250K or 500K Pot
Depends on your taste. I replaced 500K with a 250K push/pull and I can hear a pretty noticable difference. 500K => wide open, more raw tone, great for metal
250K => a bit more compressed, smoother, more of a classic rock sound now.
Split, it pretty much sounds the same, just a little thinner. The benefit of the push/pull (I know you didn't ask) can be heard in the split lil59 in the neck.
I agree, try it with what you have in the guitar already. Modify to taste.