Homebrew has the right idea. Uni bits are better suited for thin materal like sheet metal. They're pretty expensive, so if you use one go slow and use cutting fluid, same with HSS drills.
Homebrew pretty much set you straight. just start with sharp drill bits and use cutting oil, it can be purchased in spray cans. as far as angle iron, i think 2" angle x 1/4 should be ok, u don't want it bending when u hook a chain on it, also see if where you buy the angle they will punch the holes in it for you, or else you will be drilling that also.