I've not noticed license limits on the number of BGP peers. But on branch devices I would pay close attention to memory utilization on such a large number of peers to make sure the device is not stretching any hardware limitation.
There are limits generally posted for the size of the routing table and these are also driven by memory. so I would have a look at that parameter as well.
These are not hard license limits but recommended limits based on the capacity of the hardware available on the device.
Steve Puluka BSEET - Juniper Ambassador IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP) http://puluka.com/home