>>182905245 Pokemon each, to match the Gen I-IV E4 teams.
Plus a Mega each. Drasna's Garchomp, Malva's Houndoom, Siebold's Gyarados (add in a Whiscash or a Quagsire), and Wikstrom's Scizor (add in Escavalier).
In the past, the final gym leader has had 4-5 Pokemon, so it's perfectly understandable to make the Champion the first 6v6 battle of the main story, with the exception of rivals.
If you want to have a harder time against them as they are now, show up with a level 50-60 team and only use four Pokemon.
