Jessica,
1. When I make my mold I cut a channel into the rubber mold to allow the resin to enter the rubber mold. You have to pick the area that best meets your needs. i.e. That channel will need to be in the best possible spot. Example: Putting it over the face would be very bad.
2. I actually build a box about 1/2" bigger than the head using Legos. Once the box is built, I pour about 1/2" of rubber into the box and let it harden. Once the rubber is hard, I then lay the head into the Lego box with the face looking to the sky. At that point, I'll pour rubber into the box so that it passes the ears, but not quite to the face. I let the rubber harden overnight.
The next day, I cut little triangles (or cones) into the rubber within each corner of the mold. Later on, this will allow me to match up both halves of the molds, ensuring correct alignment. After the little triangles (or cones) are cut into the rubber, I treat the dry rubbers surface with something called "rubber to rubber mold release". The purpose of this is to avoid the new rubber from adhering to itself. [More on this in a moment.] Next, I pour some more rubber into the Lego box and now I can no longer see the face of the head that was starring up at the sky. I let this new rubber harden overnight.
The next day the rubber has cured. I unsnap the Lego box and I’m holding a square chunk of rubber in my hands. The mold will separate because of the coating of "rubber to rubber mold release" which I sandwiched between the pouring of the 2 mold pieces.
From there it’s matter of just removing the head and then cutting slots into the molds so the resin can enter through these channels. You probably need pictures. I’ll take pictures next time I cast a head so you can see the process.
3. No