Some of the pro's of diving with a full face mask are how it keeps your face within the mask itself, rather than exposed to what ever element you are diving in. Be it very cold water, or contaminated water, or even for folks who just have trouble getting a mask to seal when they have a regulator in their mouths. I've only seen this a time or two, but folks with very prominant "smile lines" can find full face masks much more comfortable.
The major "con" is generally it's price. Most dive masks run from $39 to $79 now a days. Masks like the Neptune mask run $389.95.
As for the first stage. I'm sure that one would work just fine, although I'd lean towards buying the mask with it's own first stage, since you'll already have it set up with the second stage.