Brood Alpha and Spy are your top priorities for gearing. Lots of CC and offense on Spy. Lots of speed and tenacity on GBA. Lots of CC on Soldier. Speed and potency on Poggle. Make Sun Fac tanky as possible.
For Geo TB using Geos you want to spread around the ability blocks by getting tenacity down and then calling the assists on to the attackers w/ tenacity down so poggle can ability block them, then move on to the next attacker and ability block that one.
In terms of most arena battles theres really not a whole lot of strategy, they're pretty straightforward. They heal a lot, have 2 cleansers, 2 taunts, 2 damage dealers, 2 buff dispellers, every attack will call everyone else to assist so you have a constant barrage of tenacity down and ability blocks. Just don't let GBA die, as he's literally the only reason they're any good.