1) If you're doing all SNMP, then there's some extra work the controller is doing that can be offloaded. The ideal communication is AMON w/ some SNMP. AMON is an active feed from the controller to AirWave w/o having to deal w/ poll requests. Client and AP updates are handled through AMON updates, and only RAPIDS and a few other lesser used topics are still polled via SNMP. (You'd see more of an impact if you're on the older Aruba controllers - the newer controllers don't can go either way but perform better when AMON is enabled)
2) You can disable polling from each group's basic tab. You override the poll period and setting polling to 'disabled'
3) Ideally, you would install the new server with the exact same version the current production server is running. Then you take the latest nightly backup and copy it into the new server. Once the file is copied, you'd restore it.
a) You get the version from Home -> Overview
b) Install new server w/ the exact same version
c) You can grab a backup from the UI on System -> Backups
c2) Or you could grab the backups from the CLI by SCPing the file to another server (option 2 [download file], select file to download, and provide the SCP target destination like: rob@10.10.10.10:/root/filestore/)
d) on new server, you use option 1 [upload file] to pull the image from the SCP filehost: rob@10.10.10.10:/root/filestore/nightly_data001.tar.gz
e) option 5 [restore] and select the nightly_data001.tar.gz file
the above will copy over all data including historical.