1. Polyester resin, this is what is commonly used with fibreglass. I use it for moulds, its fairly cheap ~£10 gets you 5 Kg. Most fibreglass seems to be sized[?] for use with polyester and if you try epoxy the resin goes white and doesn't wet the glass. I wouldn't use this with Carbon or Kevlar.
2. Vinyl esters and Phenaloics. I am told Phenaloics are good at elevated temperatures, I don't know about the strength. From what I can gather vinyl esters fill the gap between polyester and epoxy I was told vinyl esters would be OK for making moulds that had to withstand post curing or elevated curing. The price seems to be close to the price of epoxy so I haven't used them.
3. Epoxy resin, I believe the roots of this go back to a spitfire built of plastic in WWII[don't quote me on that]. Its stronger and has better temperature resistance than Polyester. For wet lay up its supplied as hardener and resin in approximately 3:1 ratio. It seems the hardeners are blended to give specific curing properties, these also affect the strength. So rather than adding less hardener to slow the cure down you use a different hardener, if you have slow and fast you can blend them to get cure times in between. If you add less hardener than necessary you can end up with a soggy mess which doesn't cure properly; the manufacturers don't give data on how far out you can be when mixing but I have only experienced non-curing when I have made a definite mistake in quantities, probably using half the desired amount of hardener. Its easy to be quite accurate with scales, syringes or the rather neat mini pumps that fit in the containers.

Mixing instructions are included with the resin, you might find "100:30 resin to hardener by weight" and "3:1 resin to hardener by volume"; These are the quantities for SP110. Often they don't quote by volume so if you used the by weight figures and mixed using syringes, a 100 cc mix of SP110 should be: 75cc:25cc. If you use the by weight figures you would mix 77cc:23cc. That's not far out about a 1cc less hardener than needed, that's OK. One resin manufacturer gave specification for the resin, hardness elongation etc., with varying amounts of hardener, the above example was within the correct mix window.

I use syringes but will buy a set of scales some time, Argos do kitchen scales for £12 they measure in gm up to 5 kg. I must admit to guessing the mixing ratio for the Pregel most of the time, I use this stuff as glue. I mix in a stainless pot that holds about 100cc but a paper cup is more convenient and rather than cleaning it you can bin it.

The main problem I had has been pinholes, imperfections in the laminate surface. After some detective work I decided these were due to air in the resin. When you mix the resin it fills with air bubbles, if you stick the pot of resin in a vacuum chamber it froths up. It takes about 10-15 minutes to pull all the bubbles from Graff SE. So I made up a vacuum mixing pot, the first was mechanical and not successful, I now just have a top for my mixing pot with an 'o' ring seal and vacuum fitting. I chuck several stainless bolts in the resin/hardener stick the top on and evacuate, then move the pot around for 5 minutes and I have air free resin, this cured the pinhole problem.

Humidity, the resin is hydroscopic[?]. If you use epoxy in the damp it goes cloudy, I assume its useless. As my workshop is a damp garage I only use epoxy between May and September and then only on dry days. I try to get any moulds done in the winter if possible so I can make the parts in the summer, polyester doesn't seem to mind the weather.

The quantity of resin to mix while using cheap poyester can just be guessed, and you either mix more or throw someaway. The ammount of epoxy will depend on the desired resin:fibre ratio, as a guide ~40% by weight is the ratio for SPS prepregs. I reacon about 75% by weight you waste some and you suck some into the breather cloth, much less than this and you find you are putting the final pieces of carbon in dry. To make this even more of a guess I guess the weight of fabric being used:)