Welcome to the forum! Congrats on the soon-to-be media room. That's got to be exciting.
I'll throw in some answers/opinions below, but IMO none of your questions will have definitive answers. You could go different ways and still be happy with the results. Luckily, matching the fronts to the surrounds isn't critical, as it will probably be tough to find a tonal match to your JBL L-250s. Btw, how does your new center sound paired with them? Also, does your receiver have auto calibration (e.g. Audyssey, MCAAC)? That can go a long way to getting the speakers to blend better.
1) My amp/reciever allows for 9.2. Are the front high speakers worth the cost and effort to add to my room?
Some people here have said they like it, while others have said that it didn't do anything for them. My recommendation is to use some spare speakers (if you have any) to try it out first before committing to it.
2) For the surrounds... do I need to look at 2-way or 3-way?
I use 2-way bookshelves and am happy with them.
3) Should I look at getting an 8" woofer or 6".
My bookshelves have 6.5" woofers and work great. What you'll want to do is make sure that the speakers you are getting (a) sound good to you and (b) play sufficiently low in frequency to match well with your subs. My NHT 1.5s are rated down to 53Hz at -3dB, which is plenty low for my 80Hz crossover point to my subs.
