Our Team Needs Help on the Drive!

[ExarKun666]

Okay, today our team decided on a drive for, what is to be our chaise drive train. the layout looks like:
|\-------/|
|-|-----|-| Front
|o|---- |o|
|--|----|--|
|--\___/--|
|oo-----oo| Back
________

(This is not to scale, the little - just is a space, so ignore them))

Okay the circles are the wheels, the back four wheels in the back will be powered on a chain, and the front two wheels will be none powered and will be held in a straight position, not free on a caster mechanism. Before our team dives into creating this, I was hoping for some feed back, this is essentially 2 back wheel tank drive. So here are my questions?

1) What advantages do you see with this drive?
2) Should the front and back wheels be powered or just the back ones?
3) is there a thread, or some specifics to way a tank drive is bad for this competition?
4) With the layout above, where would you put the wheels, which ones would be powered, and what kind of drive would you recommend for this base layout?

TY so much to all who respond, are team is rly in a fix on this, and can't rly decide, and answering these questions, would help us SOOO much, ty again!