do i have to stack fets for a 180 motor

Nope, I had one. Quick torquey little suckers. Best $10 i've spent on Xmods.

depends on what its paired with. if your just running the regular nimh batts and not an outrageous gearing no. but if you gear it up a lot or run some lithium batts i would stack them.

if this is in a truck another thing is tire size. the bigger the tire, the more strain your putting on the fets.

It depends on how many turns the 180 motor has, just like 130 size motors the amount of current varies depends on the specs of the motor.