X/Y Sand team -trying to figure out competitive battling

Question

So I've been working towards a sandstorm team but I'm not sure on a few things so any help would be appreciated. The first thing I'm not sure about is how strict roles are, as in how many I should have of each and if you should always have at least one of each. The other questions I'll address in each Pokemon's description, so I'll just go ahead and give you guys that now.

Garchomp

Ability: Sand veil
Nature: Jolly
EVs: 252 Speed - 252 Attack - 4 HP
Item: Choice band?
Moves: Outrage - Earthquake - Crunch - Stone Edge

Basically what I'm going for on Garchomp is straight power, the moves were chosen primarily based on power and coverage. I'm not sure if Choice band is the best item on him but I can't think of a better option, maybe life orb or the berry that cures confusion?

Lucario

Ability: Inner Focus
Nature: Adamant
EVs: 252 Speed - 252 Attack - 4 HP
Item: Lucarionite/Life orb
Moves: Close Combat - Extreme Speed/Bullet Punch - Earthquake/Stone Edge - Power-up Punch/Swords Dance

So I'm planning on having either Lucario or Gengar be my team's mega, I can't really decide which since they both seem so powerful. Close Combat for it's great power and stab, then Bullet Punch if Lucario is my mega, if not, Extreme Speed (since Adaptability makes them equal power). Next Earthquake or Stone edge for coverage, both seem fine with stone edge giving slightly better coverage, and finally a buff move, I wasn't sure whether Power-up Punch or Swords Dance would be better, since I might not always want to take the close combat penalty. Another thing I wasn't sure about was whether or not to make him special, with something like Aura Sphere, Dark Pulse, Phychic/Vacuum wave, and Nasty plot.

Gengar

Ability: Levitate
Nature: Timid
EVs: 252 Speed - 252 Sp.Atk - 4 HP
Item: Black Sludge/Gangarite
Moves: Shadow Ball - Focus Blast - Thunderbolt - Substitute

So what I'm going for with this is using black sludge to offset sandstorm damage, along with Gengar being a beast of a Pokemon. Shadow Ball and Focus Blast are pretty standard on Gengar, along with substitute, and Thunderbolt is there to give extra coverage. Gengar is my #1 favorite Pokemon so I always feel compelled to put him on teams, but I wasn't sure if Magic guard Alakazam or something would be better.

Starmie

Ability: Natural Cure
Nature: Timid
EVs: 252 Speed - 252 Sp.Atk - 4 HP
Item: Life Orb/Leftovers
Moves: Scald/Surf/Hydro pump - Phychic - Rapid Spin - Recover/Ice Beam

Starmie was the last Pokemon I picked so I sort of just stuffed it into what I felt was needed in the team. Water stab I'm not sure which is best but they all seem like good options, Phychic for stab plus coverage, Rapid Spin to take out Spikes/Stealth Rock (obviously), and finally Recover to heal from Life Orb/Sandstorm, Or if leftovers used I could use Ice beam for additional coverage.

Skarmory

Ability: Sturdy
Nature: Impish
EVs: 252 HP - 130 Defense - 126 Sp. Defense?
Item: Leftovers/Shed Shell?
Moves: Spikes - Roost - Whirlwind - Brave Bird

So Skarmory is here to stop any physical threats and provide Spikes and Whirlwind support. Not much to say here, I'm not really sure on the EV spread or the held item, but the moves seem pretty standard.

Tyranitar

Ability: Sand Stream
Nature: Careful?
EVs: 252 HP - 130 Sp. Defense - 126 Attack?
Item: Smooth Rock
Moves: Stealth Rock - Stone Edge - Crunch - Earthquake/Brick Break

Here he is, the Sandstorm bringer -finally. Honestly It feels like Tyranitar can be run so many ways, it almost makes to harder to see if he makes a good fit in a team. But anyway, I decided my team needed someone specially defensive, and Tyranitar gets a 50% increase in special defense while a sandstorm is up, so I thought, "Why not Tyranitar?". EVs reflect that desire although I felt it would be a waste to not have Tyranitar spec'ed some in attack so I did I split between Sp. Defense and Attack, which I have no idea if it's stupid or not. Smooth Rock is there since Sand Stream no longer summons permanent sandstorms. Stealth rock for more support, Stone Edge and Crunch for powerful stab and coverage, and then a decision between Earthquake and Brick Break. Earthquake is the more powerful move but Brick Break provides better coverage, so I wasn't sure.

So anyway that is the team I'm working for, let me know what you think about any aspect of it, I'd appreciate any help!

Summery of my biggest questions:
- Special or Physical Lucario?
- Mega Gengar or Mega Lucario?
- How to build Tyranitar
- Roles in general

Comments

I like to see Landorus back in OU, because it's basically stifled in the Uber tier, but Genesect? Hell, that thing is doing great in Ubers, and is easily the best Scarfer in the tier.

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I'm making this team for X and Y so unfortunately those pokemon are unavailable to me, I also would like to stay away from legendaries as a personal preference.

Lenub, I get what you're saying with the special and physical split, but if you look at it Skarmory and Tyranitar are not going to be primary attackers, they are my defensive pokemon, so If I take out one of my 2 physical sweepers then I'll be left with 3 special sweepers and 1 physical.

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Tyranitar has 3 physical attacks...

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True but I am not sure how to build him, which is why I put it in my summery of biggest questions, the fact remains that I would like him to be specially defensive not a primary attacker. But still I don't think I have too many physical attackers since Skarmory will definitely not be attack centered and Tyranitar will be at most hybrid between offensive and defensive.

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Hmmm.. I would put in some Fairy coverage. Try breeding Iron Head into Garchomp. Looks good though.