Your post is a mess, no offense. Like Scottsee said, you need injectors and a rewired 190 or a rewired 255 with a regulator. The good news is that your gas mileage probably won't be as bad as you think. Guys with large turbos usually have great gas mileage because they rarely enter the RPM range where the turbo is able to spool. On the other hand, the whole point of buying the Evo III is because it spools so quickly. Still, I think your gas mileage won't be horrendous. I imagine it would also depend on tuning.
It'll be cheaper if you piece the install kit together yourself, rather than buying one from a vendor. It's more work, obviously.
The turbo timer won't make your car faster
For that matter, the Greddy piping in itself won't yield huge gains.
With the level of psi you're talking about running, the upgraded wastegate is probably a good idea. Then again, the more boost you run, the less use that wastegate sees. I think it was joematttews who said that unless you have the self restraint of a fat chick in a candy store, just keep the pedal off the floor and run more boost. Porting is a good idea, but you can do it yourself, if you want to save a few bucks.
You forgot a few things. First, a boost gauge. Second, something to tune with. Third, a bigger intercooler. Assuming you tune well, you could have 350fwhp. That's pretty fast.