For your relatively small sizing, and without knowing the type of environment this is being deployed in, I would normally scope for somewhere around the following:
CPU: 4 vCPU
RAM: 12 GB
HDD: 400 GB
The AirWave application likes RAM and all of the resource needs tend to grow over time. Even with a smaller site as yours appears, 8GB would be resource constrained, and 250GB of disk space could fill up though with some records retention settings may be tweaked to accommodate. As the guides indicate, if you have a lot of new/unique client devices in your environment then you need to scale upward. The system performance tab is your friend in evaluating the health of the system - I usually check back in a few months after installation to see if RAM, CPU, HDD is meeting the needs of AW.
ClearPass doesn't add to the requirements much, but you will want to take advantage of the Endpoint Context Server function that CPPM and AW can utilize together. This allows you to jump into AW for the device directly from the Access Tracker within CPPM for a wonderfully seamless troubleshooting workflow. Here is an older link to this feature: https://community.arubanetworks.com/t5/Security/ClearPass-Tips-and-Tricks-AirWave-Diagnostic-Link/td-p/226319
In case you need to upgrade AW to 8.2.10.x, here is a post I made to help explain the process: in short, if upgrading from a previous release you will most likely need to reinstall AW from scratch and copy over an upgraded backup file.
Good luck!