I do a 60,000 mile overhaul every year. Dings, scrapes into the glass just need to be filled with epoxy. However, they may not wet out and remain white. I mix some varnish with stain and try to match the scratch area to the surrounding color if this happens with an artist brush - usually on the bottom.

As far as wether to sand it all off is up to you. I wouldn't - but if you use 100 grit for starters, you can remove most of it in no time and finish up with fine grits - you know the drill. Only you know how bad the boat really looks.

I always try to get down to glass when epoxying. I don't think it hurts if the epoxy goes over a feathered varnish edge.

You can throw it in the water the following day after a varnish. I would give it two. Don't forget, varn takes weeks to fully dry - so it's always in progress-you can smell it. This all depends on how warm your drying area is.

I'd let epoxy cure for at least 4 days (warm) before varnishing over it and scrub it with a scotch bright pad and soap and water to remove blush. I've always paddled my kayaks with just epoxy and no varn. to try them. Nothing horrible'is going to happen. I'd rather wait till it's really out-gassed before varnishing - like a week on new boat.