Honestly, if you have a well built steel frame, I wouldn't worry about it. A few small holes here and there shouldn't be a big issue, as long as they aren't in any high stress areas. Heck, I've got 4 holes in my frame. They were put there by the factory. For water bottles
I doubt putting JB Weld back in the hole is going to re-strengthen the frame any appreciable amount. I wouldn't count on the fiberglass adding any decent amount of strength either. At best it will just kind of hold the bike together if it breaks.