I have done a fair amount of repair on fiberglass boats. Floor replacement on three different boats.
I use the marine epoxy from Tap Plastics (tapplastics.com)
Epoxys use only one ratio, and you do not change it depending on the temperature. The rate epoxy cures is totally dependent on the ambient temperature. You can get epoxys that have a different rate of cure, but that changes other characteristics of the set epoxy.
I have been using their "marine" epoxy resin, 314 resin, 102 hardener, it mixes in a 4 to 1 ratio. It will set in temperatures down to 40 degrees Fahrenheit, but at those temperatures it will take overnight to cure.
Epoxy resins are more expensive. Epoxy sticks better to old materials. Epoxy resin usually does not have any solvent in it, so it does not smell, and it does not shrink. The epoxy does surface cure much better than polyester resin, although sometimes it can get a very thin oily layer on the surface called an amine blush, that can be removed with soap and water.
Epoxy resins will generate their own heat, and if you mix a large batch, and leave it in a compact container, it will start to heat up, and this will make the cure go even faster, creating more heat, and speeding the cure up even more. You can avoid this by mixing small batches, or immediately after mixing, transfer the mixture to a large shallow pan, like a bread tray, for example.
Obviously, wear eye protection. Latex gloves are fine with epoxy, no solvent in the epoxy to attack the gloves. Acetone works fine for cleaning tools, but acetone will eat through the latex gloves very quickly.
Most food containers work for mixing the epoxy, but you need to clean them out first. You can also use the "painters cups" from the auto paint store with the measuring marks on the side. Polyethylene plastic bags will not stick to cured epoxy. I have stuck pieces of 3/4 thick foam rubber inside a plastic bag to hold fiberglass, and epoxy on overhead surfaces.