What happens when you best the elite four on Pokemon red?
Once you beat the Elite Four, and your rival, you become the Pokemon champion. You've pretty much beat the game. There's nothing more for you to do, other than explore the Unknown Dungeon in Cerulean City, and catch Mewtwo, and finish filling your Pokedex. He is lvl 70, so be prepared.
There really isn't a best Pokemon team for the Elite Four. All you need are strong Pokemon, items like full restores, and Pokemon you have trained all along your journey. But, your best bet is to use your starter and maybe a few legendaries. Pokemon who are good against all the people will do as long as they are high leveled.