A couple of things to add:

MAke sure your custody agreement includes a stipulation that she can't move away (ie out of the town, county, etc..) and also the right of first refusal if she is scheduled ot have the kid but can't take care of him. This means that she can't dump the kid at her parents' for the weekend if something better comes up - she has to ask you first.

Another thing to keep in mind - although the parenting schedule will sound as if it is set in stone, and will always be enforceable during period where you and your ex can't seem to get on the same page, the reality is that you can make it a lot more flexible if you just keep the kid's best interest in mind. For instance, my husband had joint legal custody of his 2 kids, but his ex-wife got primary physical custody. As per the agreement, he had every other weekend, a few holidays, and the summer was stipulated as being "negotiable." On paper - very scary - sounds as if he would hardly ever get to have his kids. The reality was that he had them every summer, all summer. He also had them for weeks on end during the school year whenever his ex-wife just "couldn't handle it" - which was frequent. Sounds like your ex might be similar. Make sure you get a lawyer ot get you the most time on paper, but keep in mind that her character means you'll probably get your kid a lot more! good luck.