Either radio will be fine. If you move on to larger, more complex airplanes then the DX-7 or similar might be necessary but likely not for a while. Don't forget to take a look at some of the Futaba radios too.

If you go with a Spektrum, the AR-6100 will be fine. I like the end-pin version. Just cleaner in my opinion.

For batteries, go to hobbycity.com and grab some of the Zippy 3-cell, 2200mAh packs. They will fit and work great. Their $39 charger/balancer works pretty good too for the price.

You will really like the T-28. It is an outstanding airplane. I normally dislike electrics and foamies but the T-28 really is a blast.