What's the most efficient way to reduce the recoil (post-shot, not from breath recovery) on with the Barret? Is there an optimum combination of attachments / perks to use that will do this?
To my knowledge, there isn't any way to reduce recoil with the Barrett. Staying crouched and proned while shooting will certainly decrease the recoil, not just for sniper rifles, but on all guns in general.
If you want low-recoil sniper rifles try the WA2000 and the M21 EBR.
A good way of reducing recoil on any sniper rifle is to use a technique called "quick scoping". Create a class with sleight of hand pro and stopping power, you can choose any yellow perk (I would go with commando because you will be running a lot).
When you see your target, aim down sight and fire immediately when the snipe scope view appears. It will take some practice to get use to this method.
This works really well with the intervention.
Here is a video on how to use the quick scope method.