There is a lot of stuff you can do to acquire more HP.
I'm new to stangs but use to pimp out rice burning 4 bangers back in my day and while I haven't seen one, but for the 2.2L or 2.4L they had a book out, cant remember the exact name, but it was something like Hitchhiker Guide to the 4Banger. It was a thick book that listed every single part you could do to your engine to get the most HP out of it without doing an engine swap. It listed down to exactly what screws you could remove from your car to get less weight.
Since I've gotten my mustang, that street racing, pumping out my car bug has hit me again and u want to build my V6 also.
The obvious choices are start with simple bolt ons.
Cold Air Intake
Headers
Exhaust
Throttle Body
Coil
Plugs
Wires
Under drive Pulleys
Then you can move to
Aluminum Driveshaft
3.73 Gears
Supercharger or Turbo
Split Port Swap
Nitrous
Then if you want to keep going crazy
You can start removing weight
Back seat deletion
AC deletion
Remove all glass and put in plexi glass
It all depends on just how crazy you want to get with the car. Then after thousands and thousands of dollars later, you'll reach a point where the V6 just cant have anymore power, and you'll either be happy or wish you would of spent all that money and a brand new V8 build.