My cat is drooling and vocal. Is this an emergency or normal?

I am sorry Finn has you so worried today.
There are a few reasons that a young cat like Finn may be drooling.
Pain in the mouth due to a tooth issue or ulcers on the tongue or cheeks, eating something they aren't supposed to like plants or foreign objects are some common reasons.
Some cats will also drool a little bit when they are really happy. I once had a cat that would drool very small amounts when he was happy and purring like crazy.
When you take him in the vet will likely do an oral exam and try to examine his teeth, tongue and cheeks as best as they can (this can be hard to do in a cat who is fully awake). If they have any concerns about not being able to see everything they may recommend sedation to get a better look.

Since Finn is eating and drinking and as long as he isn't vomiting or acting lethargic I think it would be ok to wait for your appointment tomorrow. Be on the lookout for any other symptoms he may have and make sure to tell your vet if you notice anything. That can help in making a diagnosis.
If the drooling becomes profuse (think foamy drool all around the lips) or if he seems to be in pain or if he stops eating and drinking then I would recommend you take him in sooner.