I'm a terrible person to ask since I have little patience and so make a lousy candidate for most such debates. Generally, all of the details are up to the individuals, all the moderators do is try to chide the participants should they not follow the guidelines that THEY agree to.
Some things you should consider are:
- the scope.
- the format (limited number of responses or unlimited).
- the time frame (maximum time between post and response, usually set to be reasonably long, several days at least).
- whether or not you want a discussion of the subject to go on at the same time (peanut gallery thread in coffee house).
It's up to you two to decide how YOU want this to proceed.