16yrs old, first car advise?!

In order of actual importance as long as it runs and drives.

Brakes/ suspension/ electrical/ chassis.
THEN
Rear end, transmission, engine.

If you want to be cool and get laid. Exhaust and stereo is really all you need. You don't need to be the fastest and statistically you never will be.

Big block is more to deal with than it is worth, unless you are building a drag car. Once you chase speed, you will never stop until you or your car is broke. DO NOT SELL IT! You will not make your money back, and you will make a lot more in the future. Get a beater daily driver/ back up. Get lots of photos of the car and you. Do as much of the work yourself as you can.