1. If you take the skis, you shouldn't have to pay for the bag.? The airlines count a boot bag and ski bag as a single bag (on Delta, it was phrased as "the ski bag is free").? Even if you don't take the skis, you probably will still have to pay for the boot bag.? Also, I thought most of the airlines were $15 for the first bag and $25 for the second (I have normally paid total of $40 for suitcase, ski bag, and boot bag).
Take the Magnums, because you (or your son) may get tired of fighting all of that powder and decide to stick with groomed slopes.? The Magnums will handle the powder on the trails once it gets skied up a bit, they won't do well off-piste in that much untracked fresh snow.?
2. I like Svend's idea of trying to call ahead and reserve something.? Mythic Riders (88mm) and Dynastar 8000's are commonly available rental (or demo) skis, I also saw Watea 94's in lots of places in Utah (94mm).? There may even be ski rental places at the airport, but you should be ahead of the weekend crowd so shouldn't have trouble finding rental/demo skis.? Even normal rental shops often have "performance skis" that are recognizable models, even though higher priced.
3. Sure hope you have a 4-wheel drive rental.
Observation -- This year it seems to only dump snow when a RealSkier is headed west.? Someone must have a connection, cause all of us have hit 15" plus snowfalls.? Pretty amazing in a year that really hasn't been a huge snow year.