If I were you, I would look to get an intake and exhaust first. It will allow your Evo to breathe better. For exhaust, look to get a different O2 housing, downpipe, high flow cat/cat delete, and cat back exhaust. For the intake, you can just get a different air filter, or you can get a whole intake kit (ETS has a nice one). All of this might put you around 1000-1300 dollars.
Next, get a tune. Its the only way you're going to get the most out of the parts you installed. If you want to be able to adjust your boost with your new tune, get a manual boost controller. You can pick one up for about 75-80 bucks, or maybe even 50 bucks used. I can't tell you how much a tune costs because all shops prices are different. Where are you located? Because we may be able to point you in the direction of a reputable shop.
You could even most likely get a nice set of cams that are useable with the stock valve train. Kelford, Comp are a couple of brands that I would use for the VIII. The HKS cams, in my opinion, really aren't that big of an improvement over the stock cams. You could probably pick up this mod for about 500-600 bucks and installation is around 400-500. A nice set of cams on stock valve train can net you an additional 30 WHP!
If you shop around, you can easily get all this done for $3000. And your numbers after, with a decent tune, should put you around 320 WHP on a mustang dyno and around 350 WHP on a dynojet dyno. That right there is a fun street car for starters.
Also, if you want to get rid of the ridiculous wheel gap and do t want to spend a fortune on coilovers, pick up a set of springs. My preference, the Swift SPEC-R. They give a moderate drop and they're better than the stock springs. They're about 300 bucks and you can install them yourself.
06 GG Evo SE
I WANNA GO FAST