yes the backpack hinge can break but it usually happens when taking the FP kit(fast pack) off. just be sure to use the same amount of pull/push pressure on both sides of the backpack when attaching and removing them.
first, don't "force" anything, this is a no-no and should not be used when it comes to these toys.
the best way to get the arms through is to leave them folded like they are in fighter mode and swing them all the way out first, then fold them down into the slots your having trouble with....does that make sense?
its not tight, just snug. grab the heatshield with your thumb and pointer finger underneath the chest plate and pull it down gently. you might have to jiggle it a bit but it should slide into position without using much force.
again, don't force it. its kind of tricky but when its in battroid mode and your TF'ing to fighter/gerwalk, you have to make sure to turn the head 180 first, then swing the neck piece around 180. from there, just slide BOTH head lasers through and thats it.
theres only one thing to watch out for....
your wallet.