I've decided to put together a basic "how-to" guide that covers silicone rubber mold making and resin plastic casting. I learned quite a bit over the last several years while building my B9 Robot, Flux Capacitor and several dozen Twilight Zone Mystic Seers'. This is will not cover plastic injection molding but rather the type of molding you can do at home. Hopefully you will pick up a few tips here that will help you avoid some of the pitfalls I saw. If you haven't already, you should first check out my Silicone Rubber Mold Making - How-to Guide.
I've link to most of the necesary supplies where available at Amazon.
When molding plastic resin parts, I've uses Smooth-On "Smooth Cast 300" series (300, 305, 322 & 326) with great success. You measure it out by volume so it is pretty easy to use. It's also pretty forgiving if your ratio is off a little. I have also used a 2 part resin called Por-A Kast "Mark-2".
If you want your resin part to have a specific color you will have to experiment with some coloring. I use So-Strong colorants. There are very strong and very reliable once you figure out how much to use. To get the desired pink-flesh tone I have to mix a drop of orange with a drop of red. That is enough to tint about 4 ounces of resin. I mix up a small batch of the Part A of the resin and keep it in an air tight container.