You can use any diameter springs for that. Best to contact the cam manufacturer for a recommendation.
Are you serious? The size of the lift has nothing to do with what gears you need, it is the size of the tires, what engine you have, and what size tires were originally on the vehicle.
Honestly it depends on your tire size. But more than likely they will scrub and you will need that extra clearance. So, I'd either get a.) a body lift or b.) truck springs for the front and air shocks in the back
4 inch lift
the rims are stock size if there 15" and the tires should fit with out the lift, though its better to have the lift
The same size as the pipe it is hooked up to in the well.
I wonder why you would need that info when you just buy a new pvc valve and replace it.
Extra small hollister
Depends what size your pipe is
You need one that match your tire size and your type of valve. The tire size is written on the tire sidewall. Doesn't have to be a perfect match in width, but the right diameter is fairly important. If the valve is the same type as on a car tire, then look for a tube with a "Schrader" valve. If it's a narrow thing, it's probably a "presta" valve.
need to know the size of the engine
That is like saying what size is an automobile. Which size valve?
Need more info - what is it for? What is the size of the pipe and the pressure differences you are trying to get?