Start slow & work up to it. For one piece molds, you should be OK without the pressure pot. I use the Harbor Freight pot also & it works fine. I have a short photo how-to of a 2 piece mold I made for casting an Allison cylinder head at my Fotki site - http://public.fotki.com/cnaind/
You can make the same part from a one piece mold, it just won't be hollow. For most small parts, that doesn't matter. I also am a stocking distributor for Alumilite (20% off) & can provide phone or email support for any questions/problems that may occur. The regular tan Alumiilite has a 90 second pot life(very short) but is good for small, one piece molds. The white Alumilite has about a 3 minute pot life, which allows more time for 2 piece or large molds. There are also 2 basic kinds of mold rubber - firm & flexible. I like the firm for smaller parts (like the cylinder head). The flexible is for more complex & larger shapes (bodies). It also works best with pressure. Hope this helps.