I have used the Alumilite starter kits several times, and it's *adequate* for most casual prop purposes. A key thing to look for on the packaging is: is it the quick set RTV (tan colored) or the High Strength 2 RTV (pink color). The Super Casting Kit:
Alumilite - Products - Starter Kits - Super Casting Kit
The tan RTV sets up within 12-18 hours, and pink takes 18-24 hours. Buy a package of latex gloves, and use eye protection... but you already knew that. Follow the directions that they include in the starter kit - they are fairly well written. Be sure and have your master to be molded prepped and ready in it's mold box before you get started!
Lay out all your items ahead of time; have paper towels nearby, and use longer stirring sticks than the short crappy ones that are in the kit. Use a shop knife / Exacto to pierce the foil on the containers, and shaking them up. Consider having one or two spare masters to be molded of other things, as once you mix the catalyst into the RTV, you can't store it to be used later. I try to have small misc. items for model greeblies ready to go within arm's reach when I mix RTV, so if I get my main item submerged in rubber, and still have RTV left, it won't go to waste.
Expect things to go wrong, and you can usually avoid them. One of the biggest issues with using a boxed kit like this is that you have NO IDEA at all how long it has been sitting in that store. You can follow all the steps precisely and do everything correctly, and the RTV never cures completely. Well, it will, but it may take 14 days, not 24 hours. It's happened to me...