Other than the cold air intake, battery and security system that engine and engine bay is bone stock.
Make's me wonder why it was chipped.
The MAF sensor housing looks like it is molded into the pipe that goes into the fender-well.
A/C is not working either.
Looks like the compressor's pulley/clutch has been removed.
Might as well just remove all hardware that goes with that and save a few pounds of dead weight off the front end.
I wouldn't do headers until you find out what exactly is done with the rest of the exhaust.
Gonna have to get under the car and see what's been done.
For sound you could change the mufflers or the whole cat-back section.
The best horsepower gains are from upgrading the cylinder heads, intake manifold and the camshaft.
This is also commonly referred to as the H/C/I (heads, cam, intake).
For now though a higher flowing H-pipe or X-pipe section of the exhaust will free up some hp and change the sound too.
Everything else like headers, cat-back systems, fuel injectors, larger fuel pumps, etc. are just supporting mods.
To make the car more fun to drive though gears are the way to go.
You can do nothing to the engine and just put in a lower set of gears (higher numerically) and it will totally change your driving experience.