Hey there, welcome to the forum, ill give it my best shot answering your questions. First off, if you get your car lowered, you dont have to get new tires or new rims, its just that usually people lower their cars when they have upgraded wheels, such as 17 or 18 inch. I own a 2002 v6, and my stock wheels were 16inch wheels. I upgraded to 18 inch chrome mach ones last summer and they look great, even though the car is not lowered. The only reason people lower their cars really are to make the gap where the tire and car meet. With bigger wheels, the gap becomes larger, and to some people it might look a bit odd, but i like it just fine. Its all opinion. Some people also lower their cars for better handling and suspension etc, but that requires usually new shocks and struts for best results. Lowering springs such as Eibach or steeda or Ford Racing lower the car anywhere from 1-2inches depending on model of springs.
www.v6mustangstuff.com
www.mustangsuspension.com
www.mustangtuning.com
those sites should help with some suspension purchases or use the manufacturers websites.
Next question about what to do with your 300 dollars....2 chicks at the same time man.
If i had just $300 to throw around, i might put it into gears at this point, but i already have dual exhaust, wheels, intake and some other little things.
Once again its all opinion. It comes down to look or performance. If you want your car to have more power, id go for the dual exhaust first off...one of the best mods for v6s besides gears. Chips are nice to have, they can add some power to your car, but dual exhaust imo is the 1st mod a v6er should do. Now this means you can either get the rear exhaust..or be more unique and perhaps get a rear exhaust which costs more money though.
I purchased my dual exhaust from
www.rpmoutlet.com for 500$ shipping free. It cost me 120$ for installation at a local shop. For side exhaust, you can check out
www.stage3performance.com
which has the roush side exhaust which looks awesome, but you might need the side skirts or perhaps they could somehow cut your existing side skirts to fit the exhaust.
300 bucks tho wont really go to far for perf. or looks besides little things. underdrive pullies are a great buy for about 160$, intakes go for as little as 40 bucks on ebay, chips usually run 400 bucks depending on what kind. I would go for the dual exhaust, you can probably get one for around 300 if you looked.......good luck man
hope that helped!