In the past I have had great luck thinning the epoxy with denatured alcohol. You can make it as thin as you like. Some will argue it makes the epoxy "weak" or at least not as strong as it used to be..... more on that later.....
When I use the thinned epoxy I thin it so it wets out the cloth very easily. I have found the amount of the denatured alcohol added is not critical though I suppose you could add to much. I've gone as much as 50% without problems. I use a playing card to spread it as this is flexible and disposable. How do you know when you have the correct amount of the thinned epoxy on? Easy, if you have to much on the surface will look shinny and wet. If the cloth is "dry" it will not show the wood like the "wet" does. I know this sounds goofy but it will look dry
If you have a wet spot just squeegee the wet until you move the excess to a dry spot or off the surface entirely if needed. After it cures, lightly sand with some 120 git being careful to not sand through. Apply another coat in the same manner and if you wish add some micro balloons to help fill the weave of the cloth. Sand smooth and use your favorite painting methods from here. Back in the day I built an all wood 1/4 midget racer. Glass cloth and epoxy on everything. I came out 4 oz under the minimum weight limit ready to fly. I had to use a 500 mil battery when every body else was using a 250!!
Now about the weakening of the epoxy. IMO if you are using the epoxy in a structal aplication I would not thin it in any way shape or form. The idea is to stick the glass cloth to the desired surface. The denatured alcohol evaporates pretty fast from the mix as you are applying a VERY thin coat. The strength of this system comes from the glass, not the epoxy. A side benefit is the evaporating alcohol cools the epoxy giving you a bit more time to get it "perfect". You will find the epoxy regains it's former viscosity pretty quickly so while "cool" it may get "thick" on you. try it on a scrap piece first to get an idea of how it goes.
About that 1/4 midget... I just sold it to a guy that wants to convert it to electric. It looked as good as the day I finished it except for 20+ years of hanger rash.