This is really a Management (R80.10) question.
migrate import will work well assuming you took said backup with a migrate export.
Specifically, since you're copying from R77.30 to R77.30, make sure you are using the R77.30 version of the migration tools.
Yes, this will copy the licenses as well.
Snapshot won't work across different hardware types.
If you really want to have both active at the same time, there is a Management HA feature that will actually allow you to keep both active and synced automatically.
As for licensing, if you want to have both copies of the manager active, you'll need to have licenses for both.
If they have different IPs, you for sure will need to have licenses for both.
If one is more of a "disaster recovery" and the IP addresses will be the same, I don't believe another license is strictly required.