No help on 1). On 2) I used regular paint thinner/mineral spirits and I added some only when the varnish started to drag a little, ie it didn't want to flow as easily and felt thick to the brush. By the way I always poured varnish out of the can into another container for the coat I was working on. That kept the main varnish from getting contaminated and it eased my mind when I went to add thinner. I found a tablespoon of thinner was usually enough but I might have to do that 2 or 3 times during the varnishing of the whole kayak. Earl