I am going to be improving my engine's performance.

I'm going to begin with changing the outer components of the engine, exhaust manifold and system, intake air plentum and intake ( side note: cold intake intake or regular aftermarket, opinions? ), throttle body, fuel injection system, and ecu.

At the same time, or earlier I was thinking of changing the clutch to high performance

Afterwards, the engine pistons, and crankshafts were to be last. I am trying to figure out is it worth it, performance wise to change out the stock pistons and crankshaft with something more durable and lighter? Will it noticably improve engine output?

 

Judging by your post, English is not your first language. Not meant as an insult, just an observation. Your signature indicates that you have a B18B. The B18B responds well to modification. By changing out the pistons to a good high compression forged piston, nice gains can be had everywhere in your power band. How high depends on the fuel available to you and the availability of a good tuner. There are a few decent non-vtec cams out there, most require the use of upgraded valve springs. I had good luck with some Crower 403's on a stock B20B. How wild of a cam you run depends on your goals and what compromises you are willing to make. Good luck!