Pokemon Black Version 2

So i have been playing casually for years with my friends. Recently they all decided to stop playing, however i have unlimited access to all their stuff ( that is over 534 pkmn between us). So i decided to go pro(world champ) and was looking for tips to prepare myself for meta game. Mind you i need tips primarily about team building, movesets, strategies, item recommendations and things that i will probably see in tourny play to properly prepare myself.This is primarily bcuz while my friends and i played for fun we still ev trained some of our pokes just bcuz they were faves and so we wanted them at best. So i know how to raise em but who why and what item, move or strategy is more my issue. Any help is appreciated THANK YOU!