Backlinks and referring sites: more are better but none are necessary.
CPC and CTR: important.
Search volume and Alexa rank are gauges of possible traffic to a domain name but don't depend on them. They can appear good and then the domain doesn't have any traffic, or they can appear bad and then the domain has lots of traffic.
Traffic quality is paramount: the domain could have lots of traffic but no clicks or a tiny CPC that makes the domain worthless.
Revenue consistency is the most important: how much is the domain earning each month and is it trending up, down, or stagnant?