The Logitech G600 Gaming Mouse is an EXCELLENT tool for playing Arma 3. I use it to free the right hand and speed up important key sequences. I also use the Logitech Extreme 3D Pro joystick for flight control.
Key Mapping:
I developed and updated this keymapping over my first 3000 hours in Arma, playing a lot of Warlords, Workshop scenarios, and flying helicopters. My goal was to make control as easy as possible and eliminate any interaction with the right side of the keyboard.
The actions I use the most are on the default keys and placed to be the most comfortable for using my right thumb.
The next group of actions are on the G-Shift key set and represent less common actions and multi-key actions like telling my squad to lay down.
When I make changes to this layout I typically print the new layout and have it on my desk for easy visual reference as I relearn the new mapping.