Definitely check out Danny and hoosiers posts - you'll avoid a lot of headaches.
The only thing I would add is, shop around, or you're going to spend more money than if you bought premixed flavors. Those vendors often sell unflavored for (almost) as much as flavored. By buying 56 mg nic in pg, and mixing equal parts of straight vg, you add one step, but cut the cost of your base in half (or better).
Buying unflavored in the right ratio might be great to get you started, but in the long run, you're missing out on the whole 'saving money by mixing your own' aspect.