I just bought a 07 GT, My friends are trying to spend my money and I am just looking for a faq or sticky or user to tell me what I should mod first.

I am basically looking for what most people do and what is inexpensive to do to the vehicle.

 

Well there are no free lunches. You can only save money if you have some good mechanical ability.

Are you looking at styling mod's or performance? And what do you have a desire to do ... forget your friends, its your car not theirs. What's your price range for cheap?

 

If you are looking for better performance the best bang for your buck is a cold air intake and a tuning device. Diablosport Predator or SCT Xcal II are both very good.
http://www.diablosport.com/
http://sctflash.com
The canned tunes that they come with are an improvement over stock but get someone like Doug at Bamachips to create a tune for you.
http://www.bamachips.com/
Also...
http://www.apdperformance.com/index.html
APD does tunes for Xcal - good people to deal with.
In regards to cold air intakes, some may offer different opinions but I think most are similar however I personally think the Western Motorsports unit is best if you get their ram air box with the underhood blanket that seals it to the hood. While air flow is comparable to most other cold air intakes it does a better job of getting cold air to the engine because it draws air from the grille and is almost completely sealed off from the engine bay.
http://www.wmsracing.com/
The other thing that's good about these changes is that anyone with some basic skills can easily handle installing them.
The WMS cold air intake install is more involved than most others but with only basic skills you should have no trouble.
Other CAI kits are stupidly easy to install and most can be installed in under an hour.

These changes with a good tune can result in approx. 18 - 24 hp increase over stock with greatly improved throttle response and better overall driveability.

 

Im assuming air filter and exhaust, since it is new and I have a lifetime warranty on powertrain if I dont mod anything... I would prefer to put on what I can take off.

Let me ask you something, if I add flowmaster because I really like the sound. Should I mod the entire exhaust or will it sound good if I just do the mufflers?

 

I would say a pypes h-pipe and a nice set of mufflers like the borla/frpp stingers. If you are in that price range. It will add a little performance and make your ride sound great.

 

Typical rules for exhaust mods don't really apply to these cars because the factory exhuast is already 2 1/2" mandrel bent stainless steel and flows quite well. A different set of mufflers will give it a better sound but don't expect any significant performance gains. Different mufflers might gain 10hp at most but if you're looking for better sound by all means go ahead and change them.
As for the rest of the exhaust the only significant gain will be had by changing to long tube headers.
An x-pipe is also worth considering. These cars have an h-pipe from the factory but the effectiveness of an H-pipe is lost at high rpms. An x-pipe will give you the same benifits as the stock h-pipe but does not loose it's effectiveness at high rpms so there will be a small gain there.
Some people like the sound of an H-pipe though. With sound being such a subjective thing the best thing to suggest is to try an find someone who has a similar setup and listen.