Acetone is not needed to remove amine blush! Scrubbing with water and a Scotchbrite pad is all you need. Don't skimp on the water and you should have a good supply of clean rags. You don't want to simply smear it around with a dirty rag - you want to clean it off. If you want, you can add a capful of household ammonia to the water, but it usually isn't required. You need to be pretty careful about using solvents and other chemicals on a resin surface which you intend to re-coat with more resin or varnish. Many times subsequent adhesion and/or curing problems seem to be directly traceable to foreign solvents used with the good intentions of getting a clean bonding surface. It's just not worth the risk and they don'y yield a surface that's any cleaner than the water. If the hull is really dirty, wash it first with water and dishwashing liquid, just like washing a car, then do a final cleaning with more water, the Scotchbrite pad and rag wipe-down.
You can tell the difference between polyester and epoxy by the way it smells when you sand it. Polyester has a distinct styrene smell (like plastic model airplane cement). Epoxy has less odor and smells like ......well like epoxy - but it doesn't smell like styrene monomer or model cement. Epoxy resin will bond better to cured polyester resin than just about anything else (including more polyester resin). Polyester will stick somewhat to cured epoxy, but not particularly well and may indeed flake-off down the line.
Ribs made from doubled glass probably won't add much bottom stiffness at all. The light weights of glass used on strippers just don't have enough beef to make much of a rib - it's amazing how many layers of six-ounce cloth you need to laminate to get much stiffness, try it on a sheet of waxed paper and you'll see...
If you want or find you need to add ribs, you're probably better off glassing the inside first and then adding balsa or cedar ribs across the bottom made from half-round stock (maybe 3/4" wide and 1/2"-3/4" high) and then glassed-over with a couple strips of cloth. You glass the inside, bracing or weighting it into shape, if needed, with whatever it takes until the resin cures -including dropping the wooden ribs into the wet resin on top of the cloth, bracing them from above and letting the resin stick them down. Then they get covered with the extra strips of cloth. The ribs should taper out at the edges of the floor, run cross-wise and be spaced 12"-24" apart on the wide portions of the bottom.
When glassing the inside, if you use six-ounce cloth with a double layer over the bottom, football area and can get the hull into the proper shape while it cures, there's a pretty decent chance that no other ribs or reinforcements will be needed.