Re: Fiberglass thickness
Not a minute too soon on the stringer replacement eh?! Those thing have probably been rotting for a decade or so.
You'll get a better bond if you bed your stringers in raw and unsealed, then after your adhesive has cured out you can start your layups. Brush/roll on your first coat of resin and wait for it to tack up, apply your 1708 and wet it out. Wait for that to tack and hit it with another layer of 1708 and wet it out.
If your resin cures out between layups it'll need to be wiped down with acetone and brushed with resin again before laying more glass.