You can do anything you want to your own vehicle. It's just a matter of time, money and effort. If you don't want to make the effort, money and time is required for someone else to do it. If you don't have the money, time and effort are required to do it. If you don't have the time, money is all it takes.
Google stuff. You want fog lights? TONS of companies make fog lights. PIAA, Hella, Pro-Comp, Bosch, Cibie, KC, they all make the best fog lights money can buy.
Push bar...I Googled "2002 Pathfinder push bar" and "2002 Pathfinder bull bar" and got pages of results. Westin apparently makes a very light-duty one...
Wheels and tires? How about a wheel and tire shop? Or TireRack.com, or TruckTires.com, etc. Do you need someone to dictate what you put on your vehicle, or are in the market to think for yourself?
Go to a stereo shop for local advice. Ask them about what you can upgrade. Nearly anything can be done if you want it to be.