1987 Honda Civic Cylinder Head

Here is the scenario:
Bought the car used, drove it for about a month. Heater hose broke but it was driven for about another mile before it shut itself off. Hasn't started since. Blowing water out of #3 & 4.
I diagnosed it as a blown head gasket. Pulled the cylinder head, picture attached.

Confirm the following:
1) the head is unusable, true?

.
2) I can buy a rebuilt head for how much?
3) not sure I trust the mileage, so is it worth it to put more money into it or scrap the whole car?
4) Where did the water enter? the gasket was intack.
5) On the head, what is the hole next to the exhaust valve for? As you can see, #3 & 4 (left) the hole is corroded.

Thanks in advance.