Inline 5 power gains?

I'm about to get a chevy Colorado. Inline 5 with egr delete, cat delete, bigger injectors and tuned ecu. Its lowerd and rides really nice. It's a 5 speed. He claims it makes 270hp and it is quick but I'm buying it as a future project and want to take it to the track.
Was thinking of gapping the rings and throwing some nitrous on it, anybody have recommended jet sizes for the shot?
What other thing could I do to get it over 300hp?
How much can the inline 5 handle?
Any info will be helpful thanks.