Any advice on how/when to bring this up? Before or after family vacation? Read the book or just discuss? Email OK?
I can only tell you that my W sent me an email with 10 or so 'topics' to discuss and some of her preliminary thoughts (ex- who lives where, dating each other/others, family time, no filing for D, etc). This is taken from her email- The basic premise is a trial separation but with very clearly defined terms that we would put in place. The object is to live apart and get a taste of what your life is like without that other person and your usual routine. The hope is to clarify what you mean to each other.
She then asked if it was something I would be interested in. If not, we'd need to discuss options that I was willing to try.
If you decide to take that route, I would enjoy vacation and present it when you get back. You don't want that awkwardness hanging over you during that time.
