Hi Dave,
At a minimum you need to have 3 WAAS devices. Two Application Accelerators and one Central Manager. You need Central Manager to configure and customize the policies as per your needs and maintain consistency across the devices. In case of SSL optimization you cannot do it on the individual devices and you mandatorily need Central Manager as the SSL certificates are stored in a secure store in Central manager. In addition to this without the central manager there is no reporting with respect to optimization stats available.
Regards
Kiran.