Jump bike - low BB, short CS, sharper HA (i think) so it can take higher forks, shorter in general. Trials bike - raised BB, around 30, longer CS, 380 or so, slacker HA to take lower forks, longer - 1030 or so.
Are you undoing them much? If you just loosen them off a little bit the chain tugs will stay in the dropouts whilst you're using them. If that's not it, I'm fresh out of ideas.
Not necessarily. If the diameter's right, then it will just press in. As for removing, you knock the axle out first, then pull the remaining set of bearings out.
crash mat, landing mat, same thing. Basically, one of the principles in free-running is shock absorbing. The idea is you learn to roll out of big falls, so that you can take larger drops without getting hurt. In which case, what the f**k do they need a crash mat for, they can already survive bigger falls than usual.