The Smooth-On folks outta be a lot of help for this type of project. They have a great deal on trial packages - but you're limited to one purchase : (
One problem I found with silicon molds - was the number of repeat uses. It tends to loose its life and tear if not too careful. If your models could be cast in a harder mold - like fiberglass you'd get more castings. Something you'd have berre knowledge of.
For that application , you can use acrylic house paint, or plastic tape, or other specifically designed media to keep the resins from eating the foam. Some of these could also be used as a sanding/finishing filler on the silicone molds.
Best of luck, and