You definitely asked all the right questions. Having been very familiar with the Summit Co market for years, here's my $.02:
You'll always have an easier time renting a condo or townhome unless you buy a house that's slopeside. Advertising the house (or condo) as being on the Stage route really doesn't fool anyone - they know they'll be sitting on a bus and they know they don't want to rent your place if they can avoid it.
VRBO is certainly a good way to go. But Summit Co also has a lot of great management companies and I'd certainly look into them. Bighorn, The Managers, Americana, etc. Sure, VRBO gives you that great 80/20 split or whatever it is, but the management companies can often get you more bed nights. Be very careful of extra fees on top of the split. Sure - you might find a 70/30 split, but make sure you're not losing another 10 - 20% in fees.
How easy is it to rent during the year? Well, it completely depends on where your condo is. If it's Wildernest, good luck. If it's across from Beaver Run Conference center in Breckenrridge then you've got a good shot. I'd say if you're at a resort you can plan on about 50% average over the year if you've got a good property management company and a decent place. I'd put that near a best case.
I'd never bet on it covering 100% of the costs. Property mgt companies lie the most regarding this statistic. I don't think there's a single one of them that tells the truth. All the statistics are inflated.
And don't forget about homo association fees! They can be outrageous.
I'd recommend finding a friend who's already done this and have them hold your hand. The market can be brutal for someone who actually needs the $$$.
Finally, my $.02 on where to buy a place: somewhere within walking distance of downtown Breck, somewhere at Keystone (not managed by VR), somewhere at Copper (not managed by Copper, maybe managed by Copper Vacations). With the last two options, sometimes you can find some surprisingly good deals. For example, at Copper I've always liked Telemark Lodge. I'd shy away from Frisco unless you can find a stellar deal. Silverthorne and Dillon Valley are bad options. Wildernest.. ick.. but there does seem to be a market there for some reason.