I have a Kenwood KRC-391 Head Unit and have bought a Kenwood KFC-W300S Sub
and a Box.

How do I wire it up to the Head Unit?

What Amp would I need to get that wouldn't break the bank. Currently I have
a 30W X 2 Channel Amp in the car, would this be able to power it? If so how
would I wire it up to it?

Cheers.