There is a lot of advice out there and you need to definitely take a lot into account when making choices, but you also need to take it with a grain of salt and find your own path.
You should look more into the rules, rewards, and matchmaking for GAC, and also consider if this is the game mode you want driving your development plan. Make sure to make your own choices, and understand what your own long term plan is.
The game has a pace and its setup like a marathon, planning and patience will get you very far. Make a plan and work the plan.
As far as the direct correlation between GAC development and doing better in GW, developing a second team that is going to be useful in GAC, will help you in GW, and should go against any of the more focused advice for GAC.
