If you are diving in colder waters, the only choice is the Mares Abyss. Tested under the ice in Canada, it is the most reliable period. Other regs. are good or even great, but we have seen the least failure rate with the Abyss, and let me tell you, under the ice is like one big cave. No place to surface, no way out, except for one small hole. As far as a BCD, it's really a personal choice. A few people on this board are into cave diving and advocate a back plate and wings. Nice setup, but not the only setup. I prefer a BCD with weight integration myself. Shop around, try on a few BCD's, compare the fit. If possible, rent the models you are looking at for at least 2 - 4 dives each. As for dive computers, I tend to stick with Suunto. Again, it came down to a personal choice, but if you start down the road with computers, soon you'll be upgrading ever year or two. Then it's a sure sign that your really hooked on the sport!
On a final note, take your time, don't rush the purchase. The last thing you want is a basement full of good gear, that you never intend on using.