I am currently restoring an amdega wooden conservatory (possibly canadian cedar or redwood) which was, in its last life varnished. I am taking the time and trouble to sand down back to the bare wood to get the best results for a crisp clean painted finish.Is this absolutely necessary....? (someone said recently that you only need to get the sheen off the varnish) Also i am using a dulux flexi exterior undercoat (2 coats) but should i be using a primer first ? and what type of top coat paint will work best and lastly which type of woodfiller should be used to be compatible with those products ?