Tagged legal compliance because the GDPR to my knowledge expects those in the EU to remove unused user accounts after a reasonable period of time (I think 1 year).

"A tick box whether members should be emailed when their account is automatically deleted from the auto lurker removal" - that can be on the regular form too.

"Ideally it should run about once every 5 minutes" - I think that needs to be configurable. The timer thing is your idea, but I think it's good for 2 reasons in particular that you may not have had in mind:
1) If we email these users, we may get a bad email reputation as our bounce rate will go up a lot
2) If we have put in bad settings it mitigates the damage
I'd like to be able to have it do like 10 a day, maybe just slightly above the rate of new accounts.

"In the SQL, we might be able to JOIN on the members table with the custom profile fields for points (for the points criteria), their cached number of posts, and possibly do an internal SELECT COUNT on the action logs to also filter out those with more than defined number of actions. Ideally we want SQL to do all the filtering so we're not reiterating over members who will never qualify to be deleted." - This would be an issue on non-Conversr, but I *think* we defined delurking as a Conversr-only feature.