are the LEO rewards payouts ON TOP of the Hive payouts?

Yes

that means the total payout is 0.349 HBD + 9.2 LEO, correct?

Correct

These are two separate values; the HIVE base layer, and the hive-engine layer, correct?

Again, correct

Powering up LEO sounds like a really good idea.

Do it!

Here grab some more ;)