Freeride hardtail or even maybe a dirt-jumper would be a good choice for what you want to do for sure. To answer your questions (kind of):
1) I'd go with some good pinned platforms. Sun-Ringle' Zuzus, Syncros Mentals, Sunline V-ones or some such come to mind. But that's me.
2) It can be long - - as long as it will drop into your frame of choice far enough to slam it when you need to. (so you can put it at a comfortable height to pedal back home from urban sessioning).
3) I have no idea. I defer to others.
4) Look for burly construction and 'assault' geometry. You might even consider 26 front/24 rear combo with a fat 24 on the back - - a little more cush for dropping off things and it will slacken the frame angles a bit to make manualling easier (or so I think, since I've yet to master manualling
). Look for rear stays wide enough to hold the largest tire you want to run.
Originally Posted by kill.cactus
What exactly is "urban assault" mtbing?
You have never engaged in this brand of fun?