What type of Pokémon should I use for a future entry in a regional/international championship?

Hey trainers. I need some advice regarding my team for an upcoming championship I’m planning on entering in the future. You see, I’ve beaten the Pokémon league story with Meowscarada, Armarogue, Lucario, Zoroark, Talonflame and Tyranitar on my team. I’m thinking of using one, two or three of them in my championship team, but I need advice about what I should do with them. The list of other Pokémon I want to include in my team are Greninja, Cinderace, Koraidon, Kilowattrel, Gardevoir, Ogerpon, Quaquqval and a random legendary from the scarlet version. I hope you can give me the best Pokémon team idea, as well as some items to give them that will help me win a match and possible the championship.