No, the Babyface and the 802 have their own Totalmix, therefor the BF wheel only will interact with the Babyface Totalmix I think.
If your speakers are connected to the Babyface, then you can still adjust the volumen thru it.
Not sure what "best" means to you.
To record as much channels as possible, yes with aggregate device you can have all possible inputs available in the DAW for recording.
I personally would avoid aggregate device and connect the 802 only. One clean setup with a great interface with 12 inputs.
Aggregate device is not very stable and support is not granted.
M1-Sequoia, Madiface Pro, Digiface USB, Babyface silver and blue