Tim has good points too, and back to a Site Survey of the distance/fresnel zone/obstructions(even temporary)/type of applications (I forgot but Telnet-based/VoIP that are both sensitive), from the Office in.
The P300s are designed for Outdoor use too, so can be pole mounted above the alley traffic, but yes, managed in Standalone mode, and providing a "wire in the air" LAN-wise, so APs and users can transverse quickly. (We can fine tune P300's to find the best throughput channels)
Please consider these in your decisions too.