Yup. It's a lifetime license that belongs to you, and includes all upgrades, and can be moved to a new system/OS.
I'm glad to hear it!
And yeah, the automatic rebuild of the pool is very nice!
My upgrade worked perfectly - with the disclaimer that "upgrade" in this case meant a complete clean install of Server 2016 to a new system drive. I did however have a critical need to maintain my existing data drives.
Both Drivepool and Scanner installed flawlessly - and especially for Drivepool - it picked up the pool (once I reattached my existing drives) like nothing had happened - saving me days of time backing up and restoring up to 10TB of data.
Regarding Essentials 2016 - I would assume you should be good as well.
Sonic.