Epoxy dust is a fine filler material, I save mine, though it's mixed with outer stuff too. It's a pain in the butt to sand, so use a percentage of talc or balloons to ease sanding effort with this stuff.
I don't cut the seams with a knife after taping. I very carefully run the tape down each edge. This is one reason I use "fine line" tape, so you can bend and curve it. The crape paper tape (the blue stuff) just doesn't curve well and it's rough texture, insures a putty knife will dance around, as you pack goo into the seams, making a lumpy seam.
Multiple coats of epoxy and varnish will help smooth these irregularities out to a degree. 99% of the people looking at your boat will just be impressed, so don't sweat it too much. You're doing fine, keep it up.