I have uploaded a "finalized" V1.0 of the schematic and done most of the placement. It is looking like it will fit in 60mm x 55mm of board. Possibly smaller.
I decided to remove the 1s connector and replaced it with a right angle XT60 connector to support higher current charging. Not charging through the balance ports allowed me to get rid of the circuitry that automatically routed the power to the top cell.
I discovered that I had overlooked the high Vgs on the mosfets of the balance circuit. The original part I specced had a max Vgs of +-8V. Well below the 16.8V max that it will see with the open drain driver to ground and a pullup to the cell voltage. I have swapped the mosfet for one with a +-30V max Vgs rating.
I've also added a cover sheet with a block diagram of the system.