Might be overkill, which can be more of a problem than you might think.
Back in the 70's I went on an overnight back trip with a cheap K-Mart bag and just about froze to death. Wanting to make sure that did not happen again, I bought a Snow Lion mummy bag that had 700 cubic inch goose down with baffles and double zipper system before my next trip...rated to around 0...Should be all good, right? It was so hot that I had to unzip it all the way and tried to use it more as a blanket. Still too hot, so some parts of me were very cold all night while others were very hot. I have only used it a couple times since then and I had to go out and buy another bag to do most of my camping.
In your situation I would buy a bag rated to zero but that is not super good nor super expensive. They have some bags rated to 0 degrees on Amazon in the $35 - $75 range. I would try it out on a dry run (take it and a tent and actually set up a mock camp for an hour after dark in Long Valley after a good snowfall). Lie there in the tent for an hour reading a book and see if it's any good. If it's fine, you just saved $200 and avoided overbuying. If it sucks, you got practice setting up a tent in the snow (harder than it sounds if this is your first time - keeping snow out and things dry inside is tricky) and you can buy with confidence. My two cents.
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