Just touch up the spots you think you sanded through. Tehn snad them gently, feathering the edges of the most recently applied materila so it blends in with the earlier coats.

: I plan on heating the epoxy a bit to thin it up. I may do the Zen thing and
: hand sand the last coat. Maybe 150 grit to start?

No need to thin it. Most likely the first batch yo applied soaked way down into the pores of the wood and is still there. Thinning the last coat won't help it soak in any more. Those pores are now plugged. Thin resin will just offer more of a chance for runs and drips -- and those you'll have to sand away.

Hand sanding the resin touch ups is a fine idea. It shoudl only take a few minutes and it may keep you from going too deep. 100 to 150 grit should do. This will leave a bit of a "tooth" for the varnish to stick to. You can use the finer grit sandpapers for your final coats of varnish. No need to use them on epoxy.

PGJ