[eluser]Derek Allard[/eluser]
For someone technical, as it sounds you are, my advice would be to build with the SVN code available right now. If this is a mission-critical, ultra important project, then my advice would be to build with the stable 1.6.4 zip, although I have every reason to believe that 1.7 is solid and stable, parts of it haven't been as well tested as the current stable stuff.
No date. Sorry. It's almost universally been my experience that making those types of estimates has been a mistake - and the truth is that I really have no way of knowing exactly. The releases honestly do happen when the community and dev team think there's enough new stuff in there, and enough changes to warrant a new version. Right now, there's some really cool new stuff in 1.7 (form validation and session management are most notable) but there are many bugs in the bug tracker we need to hit first. You could accelerate the release cycle by helping verify if those bugs are legit, and offering solutions.