Good base for a E-Revo build

[miniGranis]

I am looking into building an E-Revo but need help in chosing a roller.
I will use the original tranny, Mikes motor mount and probably an 8 or 9XL and MambaMax (if the MMM hasnt showed up).

It looks like I can get an ok deal on a 2.5 Revo roller.
Q1 What would be the drawbacks (if any) when using that instead of the 2.5R or 3.3 version ?
I read something about chassisflex at the motor mount and the newer chassis has some kind of brace to support the motor mount. Would the lack of such a brace be a problem on the 2.5 ?
Would the 8XL heatsink fit without rubbing against other parts, suspension arms ?

I need to use my 2x8000 mAh (2S2P) LiPos from my Emaxx to power the E-Revo.
Q2 Would those be impossible to fit on a 2.5 chassis ?

Q3 How much stuff is needed to convert from 2.5 to say a 3.3 ?

Lots of questions but I dont want to start of with buying the wrong stuff...