Hello Maryanne,
I would recommend you to look at the KB articles regarding GPS Sync and Frequency Re-use.
http://community.cambiumnetworks.com/t5/ePMP-Synchronization/ePMP-GPS-Synchronization/m-p/37884#M1
Since you are planning to have overlapping sectors, we recommend a minimum frequency gap of 2 or 3 channel widths edge-to-edge for the operating frequencies of the overlapping sectors, in addition to the 5MHz frequency gap edge-to-edge for adjacent sectors.
Regards