Looking to upgrade my escape .25 to .257...

So after having fun with my Marauder .25 modification and so on I have decided that I want to start a new project with my Airforce Escape .25. I want to up it to a long range .257 goin for power and accuracy. I am hoping there is someone here that could walk me through what I need as info is a little hard to find on all I need for this task. 
current parts list:
heavier spring 
1. 300 bar tank overkill but doesnt have to be at max pressure of course...
2. talon tunes valve may need a different higher flow valve?
3. Barrel? more info needed!
4. hammer? Optimal weight for higher pressures?

I have the tank, spring and valve on the way.