I built a Sassafras 12 Mk. 1 many years ago, so the Mk.2 kit may be different.  However, your last question is a bit odd to me.  If I recall correctly, I filleted all the seams before I applied any glass.  In that case, you should have any worry about the unfilled epoxy you are using to laminate the fiberglass dripping through.  The sequence may have changed, but I still think it only makes sense to put in the fillet and then 'glass over it.  You might want to review that section of manual again before starting.  Sometimes you have to read ahead a bit to make sense of why you're doing something in that order.

Anyway, the initial coat which you use to laminate the fiberglass to the wood should be barely enough to wet out the 'glass just until it isn't white in appearance.  I made the mistake of being too heavy with the epoxy in the bottom of my Sassafras.  The epoxy moves with gravity, slowly but surely and when I turned my back, that extra epoxy settled into the bottom vee and floated the 'glass out of contact with the wood.  Bad juju.  I wound up grinding out the puddle of hardened epoxy and glass and reglassing a strip into the bottom about 6" wide.  The good news it worked out in the end, but the boat wound up at least 2 lbs heavier due to just that goof (excess epoxy and extra glass) and it was a PITA.

 So, start with less epoxy than you think you will need and use a plastic spreader AND a brush to spread the small amount of epoxy on a bit at a time and dab with brush end to drive the epoxy into the cloth. Sometimes the spreaders in the kit need to have their edges smoothed with some fine sandpaper so they don't snag the cloth as you go.

The weave will be prominent and I wouldn't use sandpaper at all, except on the rough edges of cut cloth, so you don't abrade the glass before getting at least one if not two coats on after the initial.  Then sand.