I looked into using just 32 pitch, 20* pressure angle gears for the initial reduction stage once.
The problem is that your design actually won't get any smaller or lighter. This is because the CIM shaft is 8mm. A 20p or 32p gear that has an 8mm bore will have a diameter of around 0.6" regardless of its pitch. Then the mating gear will need to have a pitch diameter of between 2-4", regardless of pitch again, because the speed ratio is determined by the pitch diameters, not pitch.
If you want to experience this for yourself, just make a CAD model of a basic, single-stage gearbox and see what happens.
If you wanted to have a lighter primary reduction, making the 20p gears thinner would work much better. Or you could turn down the CIM shaft, but I don't know if that's legal. I know you can change mounting, but messing around with a cim shaft is iffy.
Cutting your own gears: depends. Involute gear cutters are expensive, and for a full FRC set of cutters (20 pitch, 14.5* PA, 12-100 teeth) it costs upwards of $400. I believe you can CNC them with a small ballnose endmill, but that takes up valuable CNC time. If you have access to a wire EDM machine that would be best. Those can cut gears quickly and effectively.
Waterjetting might work too. I know my local community college used to have a hobbing machine for gears.
I use this calculator for gear strength:
http://www.botlanta.org/converters/dale-calc/gear.html
I have absolutely no idea about its accuracy, but I use it to compare the relative strengths of different pitch, pressure angle and face width gears. The most common Vex/Andymark gears in use in FRC today can withstand massive loads (such as my team's 600lb spring winch).