Welcome! You definitely can maintain a depth with forward motion, but to truly hover (zero movement up or down and forward or backward) as I understand it is not obtainable. You can give the illusion of hovering, but in time the sub will creep up or down.
We are in 2013, but the laws of physics and laws regulating bandwidth take precedence. Anyway you have the right attitude, start simple! I was taught to crawl, walk, then run. Look forward to your build and we all have had frustrations, we are here to help you.
Mike Dory used to sail in brackish water in California. He left a couple of inches of antenna above the surface and had a longer than usual delay on his fail safes just in case he did go below the surface or a wave covered his antenna. You will gain a lot of experience doing just that and it will build skills.
Again welcome to SubCommittee and this fantastic hobby!
If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.