Eero,
As you may know, on a similar sized boat, Tystie, I went from 1 mast to 2 masts to 1 mast to 2 masts, over 15 years and 85,00 miles. After all that experience, I would venture to say that there isn't a single right answer, only a compromise that kind of works for you. I think that 55 sqm is as big as I would want to go in a single sail, unless that sail is either of maximum AR or is a SJR. Then up to 65 sqm becomes reasonable to handle, but really, the 80 sqm of Peregrine is way over the top for an offshore cruising boat, though it might be fun on short passages.
So, if you go for a single sail, I would make it with as high an AR as the the boat will stand, and I think I see in your sketch 3 that you think the same. With that single sail, maybe you could put some forward rake on the mast, as was done on Fantail with the aim of not ruining the bed.
I like Graeme's suggestion of a SJR as well, but I think for this boat the sail should be of high AR, and would need 7 or 8 sheeted points, with upper and lower sheets. These are not nearly so bad to handle as port and starboard sheets on a schooner rig.
I don't see a better form of schooner rig than the one that you've drawn. The sheeting looks tight for single sheets, but not completely impossible.
On balance, I think I'd go for the single high AR sail in sketch 3 set on a mast with about 3˚ of forward rake, which should put it clear of the L shaped seat and water tank, leaving only the table to be rebuilt. On a practical, pragmatic level, the battens for this sail seem to be 6 metres long, which is sensible in terms of available materials and in manageability when rigging and repairing the sail.