This has been covered many many times before. And a wee bit of searching and reading would garner all the answers you could ever think of.
First thing....Turbo isn't your only FI option. You can SC instead. GTM do a damned good kit.
You will not get any kind of massive gains from a VQ35HR engine whilst remaining N/A. Sorry bud, it's just not gonna happen.
Most you can do - Fit 2 performance panel filters, HFC's (or Decats), get the car re-mapped with UpRev. Even then if you break 320bhp at the fly I would be surprised.
What it will do is make the power delivery smoother with a better linear delivery.
We have a few members who have spend £££££ on trying to keep NA and gain power. In the end most of them say they wish they had just saved that little bit more cash and went FI.
If you really don't want to go FI, then your money will be best spent as follows;
Premium tyres,
Uprated Polybushes,
Coilovers,
Advanced Driver Training days (such as the CAT days).