Is my party good enough to beat the elite four and the champion: Garchomp..

First put Staraptor and Dialga should be in there to also get a water type or it will get ruff and try all LV.55 or higher.

No lvl 50's won't do you'll have to get them to higher lvls

You're doing really good so far. Although I reccomend you train each of your Pokemon up to Lv. 60 or higher. I highly reccomend keeping Dialga in your team; Switch out Steelix for Dialga. The moves on each of your Pokemon are all perfectly fine.

Same as shadow916 put dialga in your party and level them up to about level 60 and make sure that dialga knows roar of time.

Thats a great team but you need to make luxray know more attack than just pure electric attacks. You should also breed another shinx and try and make it have ice beam attack so it will be a kick butt luxray once it's strong. Also try and make some of the pokemon's you are going to use a lot much stronger to stand a even great chance of not fainting. I hoped this helped.

~Twilight_Sasuke~

I beat the elite four with a team barley stronger then that but they had very good super effective moves so maybe they are

My team had:
Torterra lv 74 Giga Drain, Earthquake, Cut, Crunch
Haunter lv 42 Sucker Punch, Payback, Shadow Punch, Dream Eater
Machoke lv 36 Seismic toss, Revenge, Wake-Up Slap, Submission
Golem lv 48 Rock Blast, Earthquake, Explosion, Double Edge
Clefairy lv 38 Lucky Chant, Metronome, Gravity, Moonlight
Tentacruel lv 39 Wrap, Barrier, Water Pulse, Poison Jab

You need to take alot of healing medicine because it's very tough. Oh, I made out this chart for all trainers going to take on the Pokemon league.

This are the weaknesses of the Pokemon of the Elite Four:
Aaron
Dustox is weaek against Fire, Flying, Psychic, Rock
Beautifly is weak against Rock, Fire, Electric, Ice, Flying
Vespiquen is weak against Rock, Fire, Eliectric, Ice, Flying
Heracross is weak against Flying, Fire, Psychic
Drapion is weak against Ground

Bertha
Quagsire is weak against Grass
Sudowoodo is weak against Grass, Water, Fighting, Ground, Steel
Golem is weak against Grass, Water, Fighting, Ground, Steel, Ice
Whiscash is weak against Grass
Hippowdon is weak against Grass, Water, Ice

Flint
Rapidash is weak against Water, Ground, Rock
Steelix is weak against Fire, Water, Fighting, Ground
Drifblim is weak against Electric, Ice, Rock, Ghost, Dark
Lopunny is weak against Fighting
Infernape is weak against Water, Ground, Flying, Psychic

Lucian
Mr. Mime is weak against Bug, Ghost, Dark
Girafarig is weak against Bug, Dark
Medicham is weak against Flying, Ghost
Alakazam is weak against Bug, Ghost, Dark
Bronzong is weak against Fire

And last but not least is the Pokemon league Champion:
Cynthia
Spiritomb has no proper weakness
Roserade is weak against Fire, Ice, Flying, Psychic
Lucario is weak against Fire, Ground
Gastrodon is weak against Grass
Milotic is weak against Grass, Electric
Garchomp is weak against Ice, Dragon

All credit goes to Snowfire

No you need to get them al to level 60 at least or they will crush you