As you said, we will be going just before the resort squeezes out the last income of the year from the Golden week clients and closes for the season. Am not expecting optimum conditions
Wet snow it is then:
Wellies, good socks - fleece liners not required
Waterproof breathable trousers (over a very light base layer)
Waterproof breathable light coat over a couple of thin base layers.
Waterproof gloves.
Thin towels, full change of clothing with two sets of extra socks, swimsuit (for pool at onsen).
Cheers!