Both Livewells can be filled at the same time or one can be shut off while the other fills. My boat is also equipped with a timer on the aerator.
Recirculating pumps are available. My Livewells are 41" and 37". The back Livewells do come in a 49.5" size. Check out the video Full Livewell in a Legend SS.
The flat give a little more room on the front deck, but the v gives a better ride if you are running in a lake. I fish both lakes and rivers, so the v was my boat of choice.