The advice I'd been given was to layer and bring a raincoat. I'm bringing a waterproof jacket with an acrylic lining and sweaters. How cold does it get at night? Should I bring a wool coat too just in case?

Depends on what you call cold. We travel to Paris each November and I usually have to take the liner OUT of my raincoat.

I would stick to layers. I use a fleece vest under my rain jacket. A medium weight sweater over a long sleeve shirt and if really cold (less than freezing) maybe a turtleneck (non-cotton), with gloves and hat. Doubt if you would need the turtleneck, gloves and hat for October. But they don't take much room or add much weight.

You can expect temperatures with highs around 60 and lows about 40. However early October usually sees warmer temperatures than late October.

I think the choice of clothing depends on a person's tolerance for cool, rainy weather, which is likely.

One thing is for sure, the Metro stations and trains will probably be hot. They always are it seems.

If I were going I now I would have my Polarfleece pullover and my Goretex jacket with medium weight trousers.
I always have a rain hat, too, and an umbrella. I am not too concerned with being stylish, so to heck with people who do not wear a hat in the rain.

Last year we were in Paris in the middle of October. Carried but didn't need my leather blazer during the day. At night it came in handy.