cool team GN, don't have much to add since jimbon's suggestions were righteous.
Breloom wants a Jolly
nature. This is because after a Low Sweep you outspeed Tornadus-T switching in, which is absolutely crucial
- Low Kick: 115-136 (38.46 - 45.48%) -- guaranteed 2HKO after Stealth Rock
So if it's been weakened slightly or SR is up, you win. Since Low Sweep is the first move you'll using if Breloom switches in for free (barring if gengar's in), you can 2HKO Tornadus-T OR threaten your opponent with Spore. You basically have all of the cards this way; how cool is that? (speed tying / beating opposing breloom is also nice).
If you decide to turn Landorus-T into a tank, definitely go with Scarf Latios. It's insanely useful in BW2. (i'd run hp fire for Gene though)