Hopefully this is in the right place.
I’m hoping to use Unity to create a CCG that two people can play together online after building custom decks. I’d also like to be able to update the card database as new sets are released. Is this theoretically possible?
Yes. If you’re thinking of releasing new cards+graphics as separate downloads, you’ll need Pro. There’s also a toolkit on the asset store for typical card game mechanics.
Thanks for answering, though I don’t really have the money right now.
Then option B is to just update the whole app every now and then 
Does that mean recreating the whole thing from scratch? Or would there be shortcuts I could take?
No, it just means adding data to the main app and having people download it.
Oh, okay. That doesn’t sound so bad. Thanks for clarifying. Aside from having taken a few computer science classes in college, I’m new to programming.