Hi Lee - has the car been modified, does it have any service history - what colour is it? All of these things can impact the price someone is willing to pay
Wheel might have thrown a weight and is out of balance.
CV joint test - full lock in car park etc slowly drive forwards in circle if it has gone there will be a cyclic clunking sound also try in reverse to be sure
Yes the £20 is still up for grabs - I cant think who you mean but jfyi mods have been excluded so anything from GBit and myself is just attention seeking :D
The mountings will be the same so that shouldnt be a problem where you may have issues if it has a different AVCS setup to your own as there are single and dual versions