My Epiphanes booklet on painting advice turned up this morning, and had the distributor's phone number - Marineware Ltd. Their tech support would know best so rang them and they were very helpful.
Advised 3 coats wet on wet and then the filler. If possible do the filler when the third coat is still green so there is a chemical bond, same as the three coat wet on wet principle.
Discussed whether it was worth coating with Eposeal, a very thin seal coat. Felt this was more for wooden restorations, and would still need an epoxy primer coat on top. So advised using normal epoxy and then 2 pack paint.
Suggested SP320 would be the best eopoxy to use when the final finish is varnish. The SP320 is formulated to be very clear. We have used SP's epoxy so far to glue the boat together so that sounds good.
I asked about painting two pack paint, having found their two pack varnish absolutely no problem to apply. Advise was to make sure paint, boat, room temperature are as near to 17 degrees as possible. So a warmish dry day should be good. Also to use 5% thinners.