Kudos, Halfpass, for tackling this before there's 3 ft of snow on the ground.
I don't blanket unless we have a really
cold spell. But, my guys get positively beastie coats and are always warm to the touch when you worm your fingers into the hair. Since your horse dosn't sound like he's quite that used to harder winters, I would definitely say blanket him, waiting until he really needs it, like riccil0ve said. His coat will actually get a little better every season, or so every "transplant" horse I've ever met has.
A couple of blankets for different temps would be best (also, wash the heavyweight when he can wear the midweight, and versy-vicey), but if 2 aren't possible, I would go for a turnout style blanket, midweight (he may be a bit chilly if there's a brief temp crash, but he won't sweat and chill, which can be worse than just being cold). They're made of tougher stuff and are more waterproof. Many are designed for greater freedom of movement as well. To measure, take a tape measure and go from the center of his chest to the center of his tail, keeping the tape around the widest parts of his shoulders and hindquarters. The number of inches is the size you need. If you fall between sizes, round up one. If you do need to round up one, I like to cross-buckle the front fastenings. That takes up a surprising amount of extra space. A good fit is really worth it, though, esp. since he's turned out.
I LOVE my electric water bucket. As far as cost, it adds about as much to the electric bill as running a lightbulb the same amount of time. If you have a way to hook one up, they're awesome.
Be sure to check his feet often, my guys get snowballs in their "feathers" after turnout that can be really cold if they stay hanging in their hair. I usually end up snipping the longest "curl" off by January to be done with that. Some with lots of whiskers can get little iceballs there, too. We also remove shoes for the winter, my klutzes would kill themselves on the ice in shoes.
Other than that, make sure that his shelter doesn't let drafts in. Horses can take quite a bit of cold as long as they can get out of the wind if they want.
Hope that answered some of your questions!