To be fair, we haven't used the rentskis.com folks at Vail, only at Copper, but I have used the demo department at Vail Sports, where rentskis.com is located. They have a good group of demo people and pretty good skis.
Vail Ski Tech also has good demos. I have also demo-ed from Christy's (OK) and Gorsuch, which is expensive, but very cush and easy, and they take stellar care of their skis. Lots of out-of-country folks use them for week-long demo-quality rentals. They might be worth contacting as well, although, as I say, they are expensive (and don't have a branch in Steamboat).
I have never actually been to Steamboat, though I come from many generations of Coloradans. Gotta get there one of these days.
As for fitness, just be sure to drink lots of water and adjust to the altitude when you get here. Vail's base area is at 8,150ft, and it's very dry here, so it's incredibly easy to get dehydrated.
Snow is FANTASTIC this year. It's even been snowing on the plains last day or so, and the mountains just keep getting more. I think Vail has about two feet in the last week, on top of many, many feet in December and early January. Awesome coverage. I am actually headed to Snowmass on Saturday. Will ski a couple days there and then ski Vail next Wednesday with my Dad. Yay!