...or do you have to get your national pokedex first? I was planning on sending over some Pokemon to use at the start of the game with pokebank.
You can use it as soon as you get the Regional Pokedex.
Source: Just tested this out, I don't have the National Pokedex because I've only beaten the 2nd Gym in the game. I transferred over a Deoxys and a Shiny Ho-Oh both of which come up as ??? in their Pokémon information Dex No.
Hope I helped :)