I restored this copper pan that has exposed copper areas. I will only use it for frying fish. It's safe to use? Any advice on use/care for the exposed copper?
It is not safe. You should have that pan retinned, after which it can provide you with many years of safe use, as well as restoring its original beautiful appearance.
Exposed copper can we dissolved by acidic or alkaline foods, and over time this can result in copper poisoning, which is serious and sometimes fatal. This is why the US FDA prohibits copper(PDF) in contact with any acidic food. The Iowa ABC even banned the use of copper Moscow Mule mugs(PDF), and the FDA has advised against them.
Now, you might say that you're only cooking fish, and as a result the copper will not come in contact with acids. However, many fish dishes are finished with wine, lemon juice, or other acidic sauces, and you'd have to make sure never to use any of those -- rather limiting the use of the pan.
Get it retinned, instead.