As others have already said, you don't need closed in stalls. A good, well bedded (with straw) run-in will do just fine. One enclosure for a sick horse is nice and will provide a place to tack-up, etc. You will need to feed in the winter, but I wouldn't use hay nets. If you are feeding square bales every day, the hay is fine on the ground. It is safer for the horses and better for their respiratory systems. (I had a horse get her foot caught in the hay net). Also, feed outside, rather than in the shelters. They prefer it and again, better for their lungs. If you are feeding large round bales weekly or bi-weekly, you can get a tombstone feeder to keep them from laying and pooping on the hay.
You will need to provide more than hand watering, so a trough that you can keep full 24-7 is a must. If it freezes where you are, you will also need access to power and a trough heater. A free choice salt lick is also important. I keep mine inside my shelters so it doesn't dissolve in wet weather.
If there are no trees or anything they can get caught on, and you check the horses every single day, you can blanket them, but it isn't necessary. They will grow a good winter coat that will do them just fine. Just be sure they stay dry at the skin. (The shelter will help) Having a blanket handy with a moisture wicking cooler just in case they get soaked isn't a bad idea, but it must only be used to get them dry. Also know that a good natural winter coat proves excellent insulation and waterproofing, so snow doesn't usually melt on their backs. Riding a horse who has a nice wooly coat bareback in the winter is awesome!
I assume you are fairly new to horses (sorry if you are not), so just a quick reminder to plan for regular worming, hoof trimming, teeth and vet checks and vaccinations. It costs a little more to do these things regularly, but they are the best things you can do to keep your horse healthy and away from the vet.
Good luck and enjoy!