Audio upgrade

Starting to do the stereo in my truck. I currently have the infinity system in it now. I am going to get a double din dash bezel and put in a pioneer avh-p2400bt. I know I need an interface to connect it to the stock system. I was going to get the one that doesn't use the steering wheel controls. How much power does the factory amp have? I am going to use the factory speakers for now. And upgrade them after. What is the best way to configure the speakers in these trucks. I am thinking of front door speakers 6 x 9 and 3.5 in the dash and possibly adding a sub later. Would it be wise to bypass factory amp and amp the door speakers?