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I have fully tested Erik's procedure on a Raspberry Pi 2 with UniFi software 3.2.10. It works very well, including the configuration to have the controller start automatically on boot. I have heard that backup/restore of UniFi settings does not work in the Linux software, but replacing the data directory (/opt/UniFi/data) has the same effect.
Power wise, a Raspberry Pi 2 is fully capable of managing a healthy crowd of wireless access points. We have one that is managing about 25 of them, and the Pi's processor and temperature stay within normal operating ranges.