I don't know the "right" answer on any of this, but here is what I've had for three years now:
1. huge slab (24 x 40) we put our pool on. told contractor it was primarily for a pool but that the pool would be stored in the garage for nine months each year. so he said i do not want it totally flat. we went round and round on it a bit, and ultimately I caved since the sprinkler guy, plumber guy, and cement guy all said i'd regret totally flat. so i left it to him to slope as little as reasonable balancing my starting point of wanting flat and his for wanting drainage. I do not know how much slope i have, but i do know that the first year i noticed that in all four corners there was a "bowl" effect in that rain water collected into large puddles there. this freaked me out! but we have put a 20' round and now a 16 x 32 rectangular pool on it for three seasons now and never had a problem. we do try to center the pool on it because i think it crowns so that middle is highest and i figured if we centered it, the pool would be on a similar slope all the way around. We've never had a structural problem or really any problem. I think in year one, with the round pool, we lucked out and the side with the skimmer was a little closer to the edge of the pad and as such it was a bit lower on that side. Again, no structural problems at all. Caveat - my kids are weans and do not create tidal waves or rough-house.
2. we put foam on top of the concrete for feel and I suppose a it probably protects the bottom of the pool a bit as well. we just put the pool legs right on the foam. with the round pools there was barely any indentation even on the less-than-level concrete pad (when on perfectly level crushed rock in years prior I don't think where was any indentation). With the rectangular pool, since the walls are not upright like on a round, there are fairly deep grooves made where the legs hit.
3. I would try it for a season and see what happens - or if it is really bad, empty it after the first fill reveals a problem. Be sure to put the skimmer on the low side before you fill. I just don't know that it would be that big a deal as is, really. Also, I think some people do dig out a bit under an intex (search to confirm) so I'm not so sure you couldn't raise the feet to make up maybe 1/2 the drop and then the water would not look so uneven.