John,
Welcome to Rebreather World!! Dig in, read our articles, and scan our threads for information and pictures.
I would suggest you read a book like Jeff Bozanic's "Mastering Rebreathers" for a basic understanding of the subject. After that, try to identify what kind of diving you plan to do with a unit, and that will lead you to more specific questions that you can research here.
Again, welcome to the the best and friendliest rebreather site on the planet, and, thanks to our excellent members, the most informative!
Rob Davie
Rebreather World Admin