OK, went back and read you're wanting to do faceplates. Well, drilling large holes, like big enough for an XLR connector in sheet metal is hard and borderline dangerous. It's much easier to punch the holes, but that takes special equipment. That's probably what you saw in the electrical supplies catalog.
Definitely start with a manual center punch. If you want one of the automatic types then make sure you buy a good one (you get what you pay for). The cheap ones don't work or crap out quickly. Even with a good one there's times you'll want a plain old manual center punch and they're cheap.
For larger holes what you need is a sheet metal drill. When you try to use a regular drill on larger diameter holes it always ends up out of round (triangular). What the sheet metal drills do is, after starting in the center to locate they cut at the outside tip of the tool so when it pops through it makes the outside edge leaving a thin "washer" rather than a standard dril which pops through and then tries to expand the hole out to the final size.
If you only have a couple of holes buying the correct sheet metal drill for each size is the way to go. You might get by with a few standard size sheet metal drills and then filling in with a step drill. I've had mixed results with step drills. You could buy one and see. Sometimes it's just the thing and not a huge investment.
You can do the same thing with a center cutting (two flute) end mill. You could use an end mill in a drill press, definitely not with a hand drill. Really though an end mill is designed for a milling machine because there's no self centering function.