Rice Krispies? I have no idea how that even makes sense...
Like I said, the mould is easy. I can think of two ways offhand of doing it; one would be to mount the master in a box and pour the latex over the top until it just covers the master. Once it's set you'll be able to take the mould out, and it'll be nice and square, and ready for use.
The second, and possibly easier, way would be to simply paint the latex on. I've done this using latex glue (here, we have Copydex, I don't know what brands are available where you are); it's even supplied with a handy brush in the lid. Paint on a layer, let it dry, then paint on another layer and repeat. After a few layers, you can peel the latex off, and you've got yourself a mould.
The resin will be trickier to advise you on, not least because again I don't know what's available where you are. Your best bet would be to check out a local hobby/craft store; if there's one of any decent size near you, they'll likely have a section that deals with casting.
There's a good deal of useful advice on the subject
here - I think it was Hobbyist Prime who pointed this one out. Check out the How To section. There's also a fair bit of info if you do a search for casting or moulding (or
molding?) on these here forumses on which we lurk.