For Metagross, Go for Adamant. Max EV in Atk and maybe Spd if you want to keep Agility.
Metagross @ Life Orb (or something else)
Adamant. EVs: 6 HP, 252 Atk, 252 Spd
For Scizor, if you give it Choice Band, then you can't use Swords Dance or Roost because you'll be stuck with it. Instead of Choice Band, give it... Iron Plate or something.
Scizor @ Iron Plate
Adamant. EVs: 252 HP, 252 Atk, 6 Sp. Def
Gengar @ Focus Sash
Modest. EVs: 6 HP, 252 Sp. Atk, 252 Spd
Starmie @ Choice Specs
Timid. EVs: 6 HP, 252 Sp. Atk, 252 Spd
These 4 should be plenty.
135: "You play wifi random matchups?"
Me: "Being undefeated is fun."
135: "That's nice, but how many were against those who actually knew what they were doing?"
Me: "More than you'd think. I face one noob player per every two pros. But the point is, I'm undefeated against other RNGers."
135: "Perhaps. But the real fun comes from facing other pros in full scale 6 v 6 with no restrictions. That's where everything goes."
Moral of story: Random matchups can be fun and interesting, but a full scale 6 vs. 6 can be an epic clash where both sides bring everything they have into the field, including gimmicks, dedicated counters, and emergency responses.