#1 a shock should NEVER be used to limit your suspension travel. you can buy limit straps that work in tandem with a shock to limit travel but otherwise you will blow seals on your shocks and sometimes you can pull the shaft out of the can.

#2 there are a couple different ways to keep the spring from popping out, you can use a spring retainer that mounts to the axle and holds the spring captive in the cup, and, on even longer travel suspension, you can run a longer bump stop.

something to keep in mind.... if you were driving a truggy in the baja 1000 at 90+ mph you need UP travel in your suspension... but offroad, when negotiating obstacles at low speed, you need DOWN travel. this is more commonly refered to as DROOP. do a google search for LCG builds... that's low center of gravity. these are basically stock height vehicles running 40" tires that rely solely on droop and are very capable rigs.