If that is the way you are going to go. A donor car is highly recomended. You may get the big parts cheap. But once you install it you'd realize that you will be missing a lot of little $hit. Most of it you don't realize and it will nickel and dime you. When you tally up every thing. You will be surprised at actually how much it set you back.
By the way. On top of my head. Let me give you a list of what else you'll need besides the T5 and rearend.
Driveshaft
The 5.0 motor with everything including the ECU
Brake calipers
Brake rotors
Spindles
Tranny support bracket
Fuel pump
Steering rack and pinion
And this is just what I can come up with in just a minute.
Can you get by without. Yes you can. But I'm not driving behind you when the motor falls off the frame. Good Luck