I am running Roon from a QNAP and have decided to buy a Nucleus for my 2nd home. Which I get a free year of service. If I have the same data can I just mirror it to my new (2nd) system?
Any locally stored music or just streaming services?
6000 CD’s in my library. With another 300 or so Tidal and Qobuz.
So the first thing to figure out is (and I don’t have an answer for it…)
- can you create a backup on roon account “a” and restore the backup from roon account “b”.
This may be a problem. I’d try it for you but I only have one roon account. 
The goal here is to backup the database and restore it so you don’t have to go through the new setup, I wonder if you could just mirror everything you have, then setup the nucleus with the same account and then logout of the account and then log back in with the second account.
Is the database associated to a roon account or does the database just need a valid roon account for the roon app to access it? 
No, you can’t.
However, you can add more than one license to an account.
That should work.