Hi Steve
You have done your research as all those guns you list are pretty decent, the biggest difference of course being are they break barrels or underlevers. The BBs are lighter, but I always have it in the back of my mind they put more strain on the breach when cocking, and although the underlevers are heavier, they seem more solid - this is just my opinion, there is more to it, but shouldering and getting the feel of them is important, although I'd still go fixed barrel for target shooting as the weight advantage is kind of lost from a bench.
The difference between the compact Vs regular Airmax is length, I go for the compacts for springers due to access to the loading port, if your target shooting get something which will allow you to see the pellet holes so you can adjust your aim as required at you chosen distance, for me that's x24 version, but your call
Rest wise springers don't like bipods, they tend to jump on firing, so a heavier rest is better, I fill mine with kiln dried sand, and you may also want to experiment with different holds, as I've found that can make a big difference to your scores - practise, practice, practise, it's the only way to get better with a springer - but don't make the same mistake of keep doing the same thing 100 times if the results are not there, mix it up a bit - the number of shooters I've heard saying "I've been doing it this way for 20 years" - and thought to myself, yep, and for all those years you have still not got any better
Gun slip wise it's down to what your comfortable with as long as the slip does not allow the gun to be damaged and can take it comfortably with a scope. I only use hard cases now as I don't need to carry it around, so prefer the extra protection rather than light weight - again, your call, but I always have to have a reason for doing something - at least most of the time anyway, so try to avoid the trap of doing something because others do so - make sure you understand the "why" behind it and you will gain experience rather than be a dumb sheep.
God luck
James