every engine can and will have its problems. to say a 4mm is worse off than any other motor is a little off. a well maintained motor thats put together right can last years.
thats stupid. whoever told you that should be kicked in the balls.
yes. more power = more fun. 4mm motors can be very reliable.
by the time you buy a crank, proper porting, carbs, pipes, intakes etc. youre looking at over 1g.
that motor wont fit for shit in a banshee frame. stick to the banshee motor. itll be faster and a lot less hassle.