Cordless is nice, but you have to plan ahead and charge the battery before each use. And, if you wear it out, you have to sit around twiddling your dick waiting for it to recharge before using it again. Quite frustrating when you're in the middle of a project and your drill dies, and you have to burn daylight waiting for it to charge up so you can get back to work. If you do get a cordless, I'd also pick up a cheap corded to go along with it.
As far as boring large holes go, you can use the spade bits like others have mentioned (if going into wood) or hole saws even, but you will probably want the 1/2" if you need to drill larger size holes in metal. Although, you could maybe get by with a set of stepper bits for sheetmetal in a 3/8".
1/2" drills tend to be more powerful / full featured than a comparable 3/8" model though, and designed for heavier use in general. If I were in your shoes, I'd pick up a 1/2" corded drill, and a 3/8" cordless set if you need more portability. I own a 3/8" corded, and often wish I'd gotten the 1/2" instead.