Comfortable boots are definitely the most important part of your gear as far as hardgoods.
For the outerwear, like you said, everything needs to be the best waterproofing you can afford.
As for mid layer, I wear a mix. Sometimes I wear technical hoodies, designed to be breathable. As long as it won't hold in moisture if it gets wet or sweaty.
The same goes for base layer. You need a material that will wick away moisture from the skin. Wool, is a choice for base layer, or any technical base layer from any major snowboard company will do. The base layer is really important in keeping you warm. A lot of snowboard pants are shells only with very little insulation, so the base layer is very important.
Socks, again, moisture wicking, not cotton.
It's extremely important to have a good pair of gloves also. It's absolutely miserable if your fingers or hands get cold. I have a pair of gore tex mits and they are awesome! Just spend the extra money and get a good pair from a trusted snowboard company, it's worth it. Don't expect pipe gloves to keep you warm, they will not for extended periods. If your hands are prone to getting cold easily, get mittens. They will keep your fingers warmer than gloves.