+1 for P+D, my marathon PB was run off the back of their baby (up to 55 mpw) plan, although I did swap some of the recovery runs out for either cycling or swimming. If you've never run intervals before have a bit of a google, I don't think I managed to hit a perfect set at all during the program.
There's more opportunity to run in a ski resort than you might first think. If there are any cross country routes then these will normally be groomed, most resorts have foot paths of some shape or form. Yes, you'll get a bit puffed due to the altitude, but good training never the less.
Tried the donut bottles and didn't really get on with them, a faff to hold and the drink gets warm. I typically use either 500 ml or 750ml bottles with a sports cap and keep the bottle in some sort of waist pack. Will only use these if I'm out for longer than an hour or so. Sports caps can be stiff to open and close and are a pig to clean properly (I tend to soak mine in a Milton solution every few months as it also gets rid of the smell if I've been carrying flavoured drinks). I do have one bottle with a top like this one: