It is compatible with Mavericks. I checked your home page and you seem to be technically inclined, so I would look at the Support Page >> Knowledge Base on the site. They have several tutorials and other info posted there.
..and if you get this setup before I do, then please report back your findings.
If I remember correctly GPGtools automatically integrates it's self into MacMail. For Thunderbird I had to install the Enigmail extension. I tested the setup and it works without issues. I've also used it to encrypt files on my local system.
The only issue I've ever had, which is true for most 3rd party encryption, is I can't get any of the folks I exchange email or text with to use encryption.
Note: If you want to play with it before actually putting it into service just make a "test" key and don't bother uploading it to the key server. You don't even have to use your real name or email address if you don't want to.
As far as using Tor sites, I've never used Tor so can't comment on that.