To help you win the game, start with Torchic. Catch whatever pokemon to help you.
When you reach Rustboro Gym, make sure you have a Combusken by then that knows Double Kick. Combusken can help you througfh other gyms such as Mauville, Petalburg, and maybe Mossdeep. (If you ask me, use a Golduck that knows Surf and a Lairon that knows Metal Claw against the Twin Leaders.)
You should have no problem defeating Team Aqua with Combusken/Blaziken. Dark types are weak against Fighting type, and the Carvahnas and Sharpedos don't know any water attacks.
And you should have a fairly easy time with the Elite four, just consider weaknesses and Resistances.