A little bit of petroleum jelly (Vaseline or similar), thinned just slightly with naptha (lighter fluid), works wonders as a release agent for the RTV, and goes on thin enough not to obscure a significant amount of detail. Straight from the jar, the petroleum jelly is somewhat thick and can leave brushstroke marks if you're not careful in applying it. It's still usable that way for most of the types of plaster blocks that we use here, but if you really need finer detail, thinning is essential. Even a few percent of naptha makes it flow and self-level a lot better. For sealing a plaster "master", either some liquid soap (not liquid detergent, it's chemically different) or floor wax will do fine, and most commercial sealers are little more than a mix of soap and wax.

Making a mold is intimidating the first time or two; after that, it's not a big deal, as long as you follow the procedure.