wow...sorry to hear that...I guess your screen name says it all.
I know this sounds cliche sometimes, but I mean it: thank you for your service and your sacrifice.
I'm glad for you that R/C has had such a positive impact on you!
so getting back to the plane....
3DHS 72" Extra - there is one choice that will drive many other decisions: gas or electric? I'm gonna guess you want electric since propping a gas motor from a wheelchair is not really practical. 3DHS has a good web page that talks about the gas and electric setup options for this plane, and their recommendations are very appropriate and have met with great success.
http://www.3dhobbyshop.com/72-Extra-330SC--Red_p_15148.html
http://www.3dhobbyshop.com/72-Extra-330SC--Yellow_p_15149.html
Red or Yellow, the assembly is the same
Online pdf manual here:
http://www.3dhobbyshop.com/assets/images/3DH-72EXTRA/3DH-72EXTRA-Manual.pdf
Motor: 3DHS recommends the Hacker motor with a Castle ESC and a BEC.
The 74" Edge is setup in a similar way with similar equipment. I think one of your earlier questions was do you connect everything like the smaller electrics?
I think you are asking about the motor/ESC/BEC combination so that is what I will describe.
For a plane this size, the battery is usually connected to the ESC with a built-in BEC, or the battery is connected to a standalone ESC (OPTO) and also a BEC.
Some people even use a separate battery for the motor and the receiver/servos, in which case you do not need a separate BEC.
I'm gonna stop there and let you respond to help guide the conversation without info overload.
There are threads on the 72" Extra and the 74" Edge already chock-full of good info:
http://www.3drcforums.com/showthread.php?203-72-quot-Extra-330SC
http://www.3drcforums.com/showthread.php?94-74-quot-Edge-540
Post more questions here once you've had a chance to digest some of this info.