What do you want in the ensuite? Double vanity? Double shower? Bath? If so, what kind of bath? A separate / private toilet? I think the answers to those questions will direct you to what shape room will best meet your requirements. But, in general, a long, narrow design seems to be the most appropriate, with the shower at one end, sink/s in the middle and toilet at the other end.

i would probably try for at least 90cm but depends on the size and shape of the room, location of doors and windows and size and shape of other fixtures..can you post a plan of the room?

2500 x 900 or the 1000. Aim for 1100 - 1200 between benches.

for the banquette to be wide enough to lay on it would need to be at least as deep as a narrow single bed which makes it too wide to sit on comfortably without a very thick back rest or a giant pile of cushions to clutter up the space...why not consider a back and sideless freestanding daybed so the primary purpose is laying down and the sitting to dine is only short term and doesn't need a backrest ....this example or similar with taller legs would be a simple economical way to add the day bed feeling without expensive built ins and two along the window wall could look quite inviting with a simple throw and scatter cushion