Which guidelines should an architect use to determine how many AirWave servers to recommend?

This is the general recommendation from the AirWave Server Sizing Guide1, which provides guidelines for selecting and configuring hardware based on the number of devices, clients, and features. The guide also lists the conditions that impact hardware sizing, such as polling frequency, RAPIDS, VisualRF, and Clarity.

References: 1: AirWave 8.2.14.0 Server Sizing Guide - Aruba, page 5.

Deployed as a purpose-built hardware or virtual machine image, each AirWave server supports up to 4,000 network devices (access points, switches, and controllers).https://www.arubanetworks.com/assets/ds/DS_AW.pdf