They will both have the same seating, a mix of seating, more or less as shown in the picture further above. I was at a meeting the other day and it was confirmed. The only difference between the Met and the District, C&H lines will be the train length.
The seating arrangements will be fine on the Circle. Granted that with less doors, it might take longer to pass into the train, but there will be significantly more space inside the saloon.
Metronet have a number of set targets that they must meet and is set in the PPP Contracts; such as dwell time, journey time, passenger space and how quickly passengers can board. The more they exceed this the more cash they get.
Anyhthing extra, then LUL has to pay.
They have also not yet decided about the Chesham single and what will operate over that. It is likely though that the bay road will be extended north to an 8 car platfom.
We will know for certain in 3-4 years!