It's kind of a broad document...you might want to have an attorney draw it up or at least give you an exemplar. It covers everything from disposition of all joint property: house, cars, accounts to what is being considered separate property, to child custody and support, to spousal support. Mine was over 50 pages long and it was bare bones. Nolo Press has some good books if you really want to try it yourself.
Re: Separation Agreement...