Here is MY experience with glass and epoxy. First a bit of background. Back in the day when 1/4 midget racing was hot I built a Caudren. All wood. I used 3/4 oz glass cloth and epoxy to finish. Min. weight of a ready to fly airplane without fuel was 2 1/2 pounds.
OK, As usual I did all the steps to get the surface as good as possible before glassing. I used the 3/4 oz cloth and stuck it with the epoxy thinned a bit with denatured alcohol. I had it thin enough so it would spread easily with a playing card. When spreading the epoxy, you could look at the surface and tell if you had “dry” spots because the “looked dry”. If you had too much epoxy it looked wet and shiny. I don’t know how else to explain it.
After the epoxy cured I very lightly sanded the first layer with worn out 600 just to knock off the “fuzz”. I then applied another coat of epoxy thinned slightly more than the second. Again a very light sanding to knock off any fuzz, there was very little this time. Now I primed and painted as usual. I used lacquer at the time and it worked well.
When the plane was complete I had to add 2 ½ oz of weight to make the min. weight. I still have the Caudren and though it has a bit hanger rash it still is looking pretty good.
This technique worked well for me, but hat has been a very long time ago. I'm sure the epoxies have changed since then... I will delve back into this in the next year as I plan on building a 20% Zlin 526.