Like zippo said, you really need to get a separate balancer for your Li-Po's.. or get a charger with a built in balancer. I've got the Thunder AC6, it's a great charger and is only $55. The Onyx 230 is $80 and has no balancer..
And, I can't remember where the heck I got my Turnigy's from.. but here's some that are right around the same price:
http://hobbyking.com/hobbycity/store...00mAh_2S1P_20C
You will need to solder on whichever connector you use, as I doubt you use the style that is on this battery. Or, you can just take those dimensions listed, and go hunting.
As for your ballooning issues, I'm not sure myself. Are you on the Traxxas forums? Do some research over there, lots of guys have done different things. You could also tape the inside of your tires before you glue them together if you haven't already, that will help some.