no you dont need new rods and pistons with a p&p.
no i wouldnt get one if i was you. a port and polish to me is basically a compliment to mods that exist already.
ex. i have all the bolts ons i can get. now get a p&p to help the flow and get some extra ponies.
ex. i put a turbo kit on. get a p&p to help the flow and get some extra ponies.
ex. i dont have nothing but a cai, and exhaust. complete the trio and when you get your cam and misc valvetrain parts you have a reason to get a p&p because then your flow will be altered enough to warrant it.
by the way forget the cam gear, its basically pointless on a sohc.
so if your going the bolt on route just get the cam (and other parts depending on the cam), a header, pullies, and a vafc.