I think I need to apply more layers of fiberglass on thin spots, filler, then painting both topside and bottom.

Since you are going to repaint, you can strip off or sand (carefully) old paint where you need to do repairs. Areas where the paint is good may only need a good sanding before you prime and repaint.
Your boat was built in a female mold and the first thing that went into the mold was gelcoat - probably white hull and deck gelcoat. The deck was probably painted later (?). On the hull, you may have paint or (hopefully) the repairs were done with white gelcoat.
You need to get back to clean sanded gelcoat or bare fiberglass before trying to do any fiberglass work.
I'd (strongly) advise using epoxy resin and fiberglass cloth for your repairs. Kevlar isn't necessary and is very difficult to work with. Download the WEST Epoxy (Gougeon Brothers) Boatbuilders manual or epoxy manuals. Buy 'brand name' epoxy resin (WEST or System Three and the hand pumps for your epoxy system. You may have 'experts' tell you that you should use only polyester resin for repairs to glass boats; epoxy works better in my experience and is easier to work with as well.

After you get your glass repairs completed, you can fill the weave of the cloth and scratches/gouges with epoxy fairing mixture, and sand to a smooth surface. Then you can prime and paint.

Don't get too upset at the light shining through the hull - once the gelcoat is scraped off, that's normal. Do a careful inspection for areas where the fiberglass laminate has been damaged and worn away and concentrate on those areas first.