First of all...
Welcome Home to AFM!
I would recommend you do some reading and questioning around the V6 forums, and use the search function for your ideas.
In general terms, the smart way to mod a car is:
1. Come up with a detailed plan. Write it all down, take notes of ideas, and start a notebook where you put all that ties into the car. Research prices and parts.
2. Do whatever mechanical work on the used car is needed to bring it up to to operating condition.
3. Working from your Plan (Item #1 above), start making the mechanical modifications you want. By doing the mechanical modifications first and operating the car at the same time, you are acquiring experience and knowledge as well as polishing the car's performance.
4. I personally build cars BACKWARDS from the usual, ie, brakes and suspension first, then performance modifications under the hood or in the drivetrain, then the overall external looks, next the interior electronics (audio, video, gps, whatever), and finally interior upgrades.
If you can do the Plan BEFORE you buy the car, you might find that by shopping around for a car that already has many of the modifications or options present, you will save a TON of time and money in the long run.
"You can never be free until you let yourself go."