XDA developers is a great place, but I dont recommend it for people new to rooting their phones...
you can also go to droidforums.net, they are a little more laid back, thats where I went when I first rooted my droid.
As for the phone, I for one absolutly hate Sprint.... No offense, but I had sprint for 4 years and was sooo happy to leave them. I would stick with TMobile or go with Verizon..... matter of fact I believe TMobile was acquired by AT&T?
As for Phones. I would look at the new Bionic or Thunderbolt by verizon, although the 4G LTE isnt in all places yet, it IMO isprobably gonna be the best 4G phones out on the android system....
Although I prefer the Bionic because it is made by Motorola, Im am not a big fan of HTC phones