If your IC40 is reading within 200ppm of actual, that's fantastic. They can be way off. But so can the test kit. Both the IC and the test kit have a significant margin of error when it comes to salt. Doesn't really matter, because you can safely ignore most of what was just said about salt levels. The IC40 will create chlorine down to about 2600ppm. It starts complaining about low salt around 2800ppm. I forget the exact numbers but they don't really matter, because the IC has a "built-in buffer" for acceptable salt level. Which means, even if the salt reading is off, it's still going to safely produce chlorine while the low salt light is off. Once it turns on, you still have a way to go before it will stop producing, but that's the "early warning" to adjust salt. Running it higher won't make better or more chlorine. Temperature will come into play in the colder months, so you might end up needing more salt, but not until that Low Salt light comes on. That said, there's nothing wrong with 3000, or 3200 or even 3400. Except...
Pools collect salt. Salt leaves a pool only by replacing water (including rain that causes overflow), flushing water, or splashing it out. Liquid chlorine, muriatic acid and humans all leave salt behind. Which is why for many pools excess salt will necessitate a water exchange at some point. So don't add salt just to satisfy an arbitrary number, or you're going to get to the excess level all that much sooner. If your test kit reads 2800-3000ppm, and your IC is not complaining about low salt, then you have enough salt. If it gets cold and the Low Salt light comes on, then add a bag. Simple.
Adjusting the SWG to zero is fine. I unplug mine, and wrap the plug in a zip-loc bag to keep it dry. One method isn't particularly better than the other. I like the idea of powering it down. Perhaps that saves the electronics from early failure in some small way? Can't hurt. Powering down my IC also powers down my IntellipH, so that's another set of electronics I let rest during the winter.
IMPORTANT: If you decide to unplug your IC, be sure all the breakers to the pad are off first. Do not unplug anything on your pad while the circuit breakers are on.
I don't shut down my SWG until it won't actually produce chlorine (as indicated by the Cold LED). If yours produces chlorine year round, then run it year round. Why wouldn't you? I would, I just can't.
While the SWG is active, your CYA should be 70-80. Period. Use the 80 end of the range if your weather is especially hot. If it's 40 now, that's fine if your SWG is off. I don't even monitor CYA in the winter (because my SWG is off), I adjust CYA in Spring when I turn my SWG back on. If it drops to 60 in the winter, so be it. That and the colder water maintain my target FC (of 5-7) for a week at at time just fine. If you run your IC year round, then keep it at 70-80 year round.
Some of these points could be argued. I would only argue this: I know they work! Other MOs might work just as well.