Well, I don't have water at my coop either, (been this way for 40 years! lol) and have to haul it down. Hilly property, winter snow and ice can be a pain. As far as hauling down feed, I use a children's sled when there's snow, or even just frozen ground. I get a cheap plastic one, that may or not make it to the following year. Summer I use a wheelbarrow, but winter, go with a sled. I have access to water not -too- far away, I can run a hose most of the year, but for winter, I haul it in two buckets, each about half full for less slopping as well as better balance.
If that's too much for you, you could save gallon jugs, fill them and drag them on the sled too.
As far as winterizing walls and windows etc, without more info about what your coop is like, that's kinda hard to say.
This year, I am going to get some of that foam-core insulation boards and lay them in the rafters, as a sort of 'baffle' for air circulation. There will still be air going up to the upper vents, but it will be shifted around the insulation which will not be 'tight'. I'm not sure why I think this will help, it just seems right, I'll find out and I can easily shift it around or remove it if need be! I've been blocking lower cracks and crevices etc, the pop door may get some of those plastic curtain slats to baffle incoming cold too, (like they use in grocery cold rooms). This is a new coop in the same old location, so I'm going to have some learning room all over again. (old coop was just too far gone, went for some years unoccupied and neglected)
hope that helps and others will have some ideas too!