1.How does having different weight distribution affect driving torque ?
Torque is a measure of force coming from the motor, so it won't be affected, in other words, if stall torque of the motor is 3N.m, it will be the same no mater how disbalanced Your bot will be. However, it will have affect RPM of each motor, so if right side of the bot is heavier than left, right side motors will have to work harder and hence at lower RPM, that is, if there's no feedback system in place, Your bot will drift to the right. Other thing to consider is traction, heavier side will have more traction than the lighter one, again, that might cause drifting.
2. Though 4 wheel drive provide better acceleration than 2 wd , what are tg
The drawback ?
Higher power consumption, hence shorter battery life Price, as 4 motors and feedback circuits will cost twice as much as for 2 motors and their circuitry. Bot being heavier.
3. Will powerful motor always guarantee faster acceleration ?
[...] faster acceleration than what, less powerfull motors? If You have Corsa with 1.3 CDTI and other same size Corsa with 1.7 CDTI, which will have more torque and higher acceleration?
Note: I have 1.3 Corsa