I have music at home and my office (same music but copies in two locations on two separate networks, same Tidal account, etc.).
Is it possible to use once license to set up two cores, or do I have to pop for two licenses?
Which in summary means 1 license if you don’t want to use both cores at the same time, and 2 if you do 
Outstanding. Thank you! I’ll give it a shot when I get home today. And basically, each time I log into one core, I disconnect the other one?
Yes. It will deauthorise the other for you.
Even better now that Roon has sorted out the back up of the Roon library in 1.3 you can move your edits between the two Cores without replicating the extra work.