I think I have decided to purchase this:
http://www.graysonhobby.com/catalog/...tor-p-772.html
to power my electric converted Hobicco Superstar nitro trainer plane.
My question is do I need a UBEC? I believe I do as the lipo will also power the electronics. Which one though?
http://www.graysonhobby.com/catalog/...bec-p-786.html
or
http://www.graysonhobby.com/catalog/...bec-p-876.html
I'm hoping this is enough power for this plane. I will be running 2 2s 5200 30c lipos in series to start and purchasing a couple 42 3700 20c lipos soon.
Thanks for the help...

Yes, you need the UBEC to power the onboard electronics. The 3-amp version should provide more than enough power unless you will be running a large number of servos, and digital ones at that.

Your plane appears to be well powered with that system. The batteries listed will easily provide the necessary current with less than a 10C draw. Good luck with your future flights!