I read through your project scope and think you are looking to create something(s) that pretty much already exist. I also don't believe some of your premises to be correct....for instance your project scope states:
"Current solutions like a full-face dive or snorkel mask have airspace that increases the buoyance of your head but the rest of your body sinks which makes it difficult to be horizontal without equipment that increases the buoyancy of the lower portion of your body."
Whether or not the mask increases buoyancy, the composition (ratio of muscle, fat, bone, etc) of the rest of the body will impact the positive/negative buoyancy of the upper and lower body. The amount of buoyancy a facemask (full face mask or snorkel mask) adds can easily and readily be balanced with current off the shelf balasting products.
You also wrote:
"My adapted mouthpiece for scuba diving and snuba diving will be better than a traditional full face dive mask because the adapted mouthpiece will have no empty air space allowing the user to go into a horizontal face down swimming position without the need of a wetsuit and/or flippers."
I think you are putting way too much emphasis on the effect a traditional full face dive mask has on ones ability to attain/maintain body position in the water, and while a wetsuit and flippers can affect body position in the water, they are not employed for that purpose. As you may/may not know, a wet suit's primary function is to provide thermal protection, and flippers are primarily employed to provide a more efficient means of propulsion in the water compared to using bare feet or the arms and hands. The employment of a mask, whatever the type, would be independent of the decision to wear flippers and exposure suit.
Currently full facemasks exist, and so do straps to retain a mouthpiece in place.
There is already a limited market for much of SCUBA gear, and given much of what your project scope discusses already exists in some form or another, it would be more effective to adapt and use existing equipment than to engineer something with limited marketability that is designed to address perceived problems that don't really exist.
-Z
