Re: varnish in cold weather?
With low humidity, I've had excellent results brushing traditional varnish (specifically Pettit BAK-V-SPAR) in the garage at temperatures in the 40's. However, I have only done this with pieces small enough that I could carry them into a warm, ventilated and heavily newspapered bathroom for curing. I got some very flat, heavy coats that way.
I haven't tried this with the Flagship varnish I'm using currently.
Years ago I brushed an evening coat of BAK-V-SPAR outdoors when temperatures were in the upper 50's. Humidity was low and it came out fine the next morning.
"Whiskey is for drinking, water is for fighting over." -Samuel Clemens