[acidrain]

Welcome! Wow, good questions... I'll try to answer each one, and I'm sure others can chime in with thier comments too.
First of all, cast parts do not ano well. Others here have more experience than I, but mainly, the smut (because of the alloy) is a problem, and often makes the part turn out blotchy or dark.
Battery chargers don't work well because they are somewhat low in voltage, and some way of adjusting the current is needed, which is a project in it's own. The mastech units you are looking at is what I use, and work fine. I've had one go out on me, but it was covered under warranty.
Yes, you turn the volts up all the way, and slowly ramp up the amps to your target, and it will hold the amps and the volts will just do what they need as the resistance changes during the run.
As for your current density, don't go below 4.5 amps per sq. ft. I use 6 A/sq. ft., which works well.
Doing freshly machined parts is a cake-walk. Just be sure to use anodizing specific chemicals... de-smut, degreaser, dyes amd sealer. If you know the alloy, even better (some alloys ano quicker than others).
Hope that helps.