If you do all your fill coats after the glass wet-out you'll have a chemical bond, but you must follow the epoxy instructions for the specific epoxy you are using, for the time frame of when you can re-coat without having to sand. Nothing wrong with a mechanical bond you just have to clean off any amine blush and sand first before re-coating.

If you cut out your cockpit coaming and hatch openings using a sabre/jig saw use a 32 tooth blade for a smooth cut.
Also score the cut line first with a new utility knife blade to break the glass threads, so the up stroke of the sabre/jig saw doesn't pull up the glass strands before they break and leave an edge of delaminated glass along the cut.