What problems are encountered when using a motor attached to the cranks?

Does the chain get streched?
Is the transmission loss roughly equivalent to spinning a hub motor?
If the motor is on a full suspension bike with the lifespan of the motor be increased to to it not being jarred?
Does the motor pull on the rear derailer cogs/rings?
With a crystalyte x5 running at 72 volts would it tear apart a geared hub?
Sorry for all the questions, thanks for your help.
I bought a khs full suspension steel frame, in searching for a steel framed full suspension bike, I came across the following: 1998-2000 jamis dakar sport's are steel, the comp and the expert however are alu, also gt made the lts-5 in steel but the shock is difficult to find,and of course the one i bought a khs pro xc. The advantage of these frames are that there is no movement in the front triangle, except the dakar has the shock at the top tube like a titus.
mike