Step 2: Handy Tools to Have on Hand
So, why de-gas your silicone and pressure cast your resin? Pressure casting yields much better results than "gravity casting" or casting at atmospheric pressure. Molds that have fine details will almost certainly end up with bubbles in the castings - either from air entrapment, surface tension issues, or moisture in the mold (resin+water=foam). Casting under pressure (80PSI in my case) basically "crushes" the bubbles down to almost nothing - or to a size much much smaller than they would have been without it. Of course, this same phenomenon (crushing the bubbles) ALSO works on your molds - so if your mold has bubbles below the inner contact surface, those bubbles will be "crushed" and will produce bumps and bulges in the surface of your casting - so - if you want to pressure cast your resin, you need to have bubble-free molds to go with it.
If you aren't going to pressure-cast parts, you can skip the compressor and pressure pot. If you are going to use a mother-mold system, or, some of the thin-viscosity mold-making silicones (less durable but easier to work with) then you can forgo the vacuum chamber and vacuum pump. What you choose really depends on your end goal and what you're willing to put up with in exchange for your time and money (Isn't that the case with just about everything?)