Number 1: You should probably just use a regular old drill. The dremel is not really designed for punching through heavy materials. Drilling through cast aluminum at 35,000 rpm is prolly not the way to go.
(I know, I know they're usually variable speed, but it's not as funny if I don't exaggerate.) (Not that it's really that funny anyway.) (Please move on to the next paragraph now.)
A center punch is an easy cheap way to avoid bit travel as you describe. If you're really in a pinch, find a nail and a hammer, you just want some kind of indentation, and the drill bit will find its way home.
Unibit: Never used one, but I have heard unanimous unconditional "yay"s as far as they go for drilling Hammond boxes. I imagine they're very convenient, as they take a lot of work out of "stepping up" the hole you're drilling.
Especially when you start getting out to larger diameters, like the 1/2" stomp switch hole, lubricant is a very good idea, and will save you money on drill bits in the long run.
Slightly OT, but if you're willing to sink a little money into this hobby, a honest-to-gosh-drill press is a *great* thing to have, if you have the space. You might also be surprised at the price - I ordered one online from Grizzly - $75! It's occasionally a little on the small side, but it gets the job done generally speaking. I went with the 10" model and I've been generally pleased...