: 2) does varnish need to go onto a mirror like finished surface - or can it be
: the final saving grace to achieving a perfectly gleaming hull?

The varnish needs to go on a sanded surface in order to bond. Sanding out the runs, low spots, and squeegie lines is part of the pre-varnish sanding.

If I understand what you are saying, you don't want to apply it to a "mirror like surface" or clear shiny surface. You want to apply varnish to a completely smooth and fair surface that has been sanded. It will look dull as sanded epoxy looks. The varnish will give it back that shine and clarity.

Hope this helps