As for Aggron, it's not the best competitive pokemon ever, but it's usable from the looks of it(assuming you're newer competitively, seeing as you just asked me about this). If it's for stealth rock, I'd go for a combination of Sturdy and Metal Burst. It's actually usually best with Rock Head/Head Smash along with Automize and EQ, though that's not usually the best for setting up Stealth Rock, but I could see a move set of Automize/Head Smash/Earthquake/Stealth Rock. I've actually never touched an Aggron in my life, so I'm not any expert on it.
Starmie usually has a simple set. Surf or Hydro Pump, and then Thunderbolt and Ice Beam for the "boltbeam combo", as very few pokemon resist both Ice Beam and Thunderbolt. After that, just a simple rapid spin. You can give that leftovers or life orb. Life Orb boost the power by 30%, but leftovers is what I generally prefer because it has no recoil. Timid, along with max special attack and speed is what's generally best for it's EV spread.