Pokemon Platinum Team to beat the E4 a second time?

I trained to fight the E4 a second time. This is what I run:

Empoleon- Lv. 76; Surf, Flash Cannon, Ice Beam, Toxic @Metal Coat
Abomasnow- Lv. 76; Ice Punch, Blizzard, Wood Hammer, Substitute @Leftovers
Houndoom- Lv. 76; Fire Blast, Dark Pulse, Flamethrower, Nasty Plot @Flame Plate (Switch to Dread Plate before Lucian)
Luxray- Lv. 76; Thunder Fang, Thunderbolt, Return, Crunch @Magnet
Gengar- Lv. 76; Psychic, Shadow Ball, Sludge Bomb, Focus Blast @Life Orb
Garchomp- Lv. 80; Earthquake, Dragon Claw, Crunch, Stone Edge @Choice Band

Do you think I'm ready?

I think so. You're just a bit overleveled, which should give you a comfortable margin - particularly if your pokemon are EV trained well. The movesets all look good.