I haven't come across a place on the forum that people can post contracts, I think this may be a good idea. No post can be edited. Might make some things feel more official. Very little difference from what happens now, but I think people would feel more obligated to fulfill their role in this more formal setting.
Use GPG keys to sign a message, then have a 3rd and 4th party quote it in the thread. Problem solved.
Yes, but it would be nice to have a place to put (and find) all the contracts.