Justin,

I would suggest taking care of the vacuum leak problem RIGHT AWAY.

If you've got a vacuum leak that is bad-enough to cause a "loud hissing" and raise the idle to 1,500 RPM--that's a BAD vacuum leak. You had asked if the hissing and the high idle were related--definitely, they are.

A vacuum leak that bad, I will assert, my ruin your engine within short order.

STOP DRIVING THE CAR until you have fixed that problem.

Did you spend the $4,000 on top of the purchase price?

Concerning the electrical issue, you are going to have to trace-down each circuit to find the specific issue. People can suggest possible areas to look (like grounds) but there is no chemical spray that will magically solve electrical problems.

It sounds like this car is in a world-of-hurt. Parts are missing. A bad vacuum leak. Electrical issues. And, it doesn't sound like you are too familiar with the car (given your poor descriptions).

I think the best thing would be to find someone competent who can work on the car for you.