New rule
Use {name} anywhere to greet them by name.
When
Comma-separated. Matched as whole words, any case.
A rule for one post wins over an every-post rule with the same keyword.
Public reply under the comment
One is picked at random each time, so replies don't look copied. Leave empty for no public reply.
Then in their DMs
Meta allows one message in reply to a comment until the person writes back, so end the first message with a nudge like "Reply YES".