It looks like you decided to get the rat terrier from the person who's moving. I've owned a lot of dogs, loved them all, but my two rat terriers I've had special bonds with.
1. 60 degrees isn't so cold for a rat terrier. I have a coat for mine but we're near DC (we were doing an agility run-thru today and it was 28 degrees when we started--ice on the ground--he was fine during the run-thru and only needed his coat when we were standing around). If you do get a coat for him, beware of sizing. A rat terrier typically has a big chest and lots of tuck-in (ie: dog-speak for "no belly"). So sizing is an issue. If you feel you really need a coat, look at Foggy Mountain coats. They are all hand-made, all in the USA, I've met the owner, they make special sizes (like for greyhounds and bulldogs) and her stuff is top quality. URL is here: http://dogcoat.com/
2. No, neutering at 9 months is not too soon. Ideally you want to do it before your male starts raising his leg. It's probably too late at this point. And it's good of you to neuter him as well.
3. Compare to a JRT? Almost no comparison. Both are terriers. Ratties are often mistake for JRTs. But Rat Terriers have a thinner, shorter, less coarse coat, smaller muzzle, bigger chest with more tuck-in, longer ears, a longer tail if it isn't docked, longer legs (unless it's a Type-B Teddy Roosevelt version of the rattie) and bark a lot less. I like to tell people that a Rattie is a JRT with an "off-switch." Very athletic, good at tricks, very hardy. But it's not constantly "on" like most JRTs are. For instance, my rattie is wrapped up in a blanket and sleeping next to me on the couch as I type this.
Temperament differences? Varies a bit with the dog but generally speaking, both JRTs and Ratties will dig but Rat Terriers generally don't "go to ground" like JRTs do. They don't bark as much EXCEPT for what Nicole said: they are absolutely perfect alarm dogs. They notice when strangers come by. In fact, you might find this to be a problem. The best advice I can give you is to REWARD your rattie for barking at the door. Usually, they're barking frantically and when the human reprimands them, the rat terrier gets worse because they're frantic--they want you to know there is a possible intruder or stranger out there. So the best tactic is usually praise and a treat and the dog goes "good--my job is done here!" and calms down. But absolutely rat terriers are an alarm dog.
In terms of activity, they need physical activity. But give them a good walk or a sport like flyball and they'll spend a big chunk of the day sleeping or lounging in a sunny spot. The other thing you'll find is that they need mental stimulation. So tricks, playing, a sport that requires them to think, obedience classes--all of these are good for your rattie. And you'll find that he's a very fast learner and probably superb at tricks.
Also, all dogs like to be around their humans. But rat terriers are notorious for connecting with their human family and preferring to be around you versus other dogs. Don't get me wrong--they'll play with other dogs. But if you are okay with this, your rattie will almost certainly want to climb under your sheets at night and sleep next to your feet. The best way to calm a rat terrier down any time is to wrap it in a blanket like a burrito--completely covered. Something about being wrapped up calms the breed and encourages sleep.
As someone else pointed out, many rat terriers are a bit skittish about people petting their heads. I've seen this with enough rat terriers to know that there is some genetic influence here. It may have to do with smaller dogs perceiving threats from above and also why cover is so reassuring (no-one can attack you from above if you're covered or in a cave or den).
4. Other Rat Terrier advice? First, especially if you've got a toy or miniature rat terrier (under 16 pounds), you may want to be careful about birds of prey. My rattie was bred in Florida. I was told by the Florida breeder that hawks and eagles will follow them along. I've never heard of a story of a rat terrier puppy being swooped up by a hawk. Another breeder told me that it was true the birds followed but it's because the rattie puppies would flush out prey for them. So just keep those issues in mind and then evaluate for yourself. If you've got a fence, make it so it's not easy for your dog to dig out under it. We basically buried rocks and aging timber under the base of the fence so our guy (who dug under it twice) stopped. Always have some appropriate chew items available (so your rat terrier has an acceptable outlet for chewing on). You'll find your rattie probably likes to engage in tug games. Stuffed toys probably won't last long--my guy has pulled out the stuff on things like toy rabbits or birds in 2 minutes after getting them. So we tend to stick to ropes (for tugging), various kinds of rawhides a