Kyogre should have no issues trashing the Elite Four on its own. Just run Surf, Ice Beam, Calm Mind, and Thunder (100% accurate in rain). Rain-boosted Surfs cream most of the mons but your coverage options will deal w/ stuff like Walrein, Salamence, etc.
To be honest, the rest doesn't really matter, so I'd use the mons that you think are cool or cute or whatever floats your boat. Because as long as Kyogre isn't criminally undertrained, it's gonna massacre everything.
Also, teaching Gardevoir Thunderbolt is definitely a good idea since its coverage with Psychic is pretty good.
Why are the beautiful sick and divided like myself?