I know this is not exactly what you asked for, Hern, but as a suggestion for first time/ part time players I would venture the idea of not having any permanent rules in place until both of you know a bit more about how intense you want your play to be.

It is great that you are able to talk about it, and if anything, the first thing you should have in place would be a safeword to be able to stop the procedings if any of you feel like things are getting too intense.

Also useful is a "playword", a specific sign or word that will indicate to her that she should conseder herself "in role/characther", henceforth.

Another suggestion: Have your sub do something, anything for you as her master, every day. Whatever she decides to do will give you an even clearer idea of how play will be conducted.

This has worked very well for me and my boyfriend F. since we started into this lifestyle. To this day we do not have any permanent rules other than me being forbidden NOT to use my safeword if I need it. The constant improvisation keeps me on my toes and enhances our creativity.