My understanding is that the AFC version ( 2 x doors, 2 overwings, one type B door) is required to take capacity to 240, so I think AFC will be required for LR and high density versions.
Yes. AFC is lighter than the old (current) door layout and allows for more flexible premium cabins so it is standard on the LR, and of course needed if you want 240 seats versus 230. Right now Airbus is offering both to airlines (who don't need the 240 seats or are not getting the LR) but I believe the long term intention is to convert fully to the AFC layout (probably by slowly raising price of current door layout option to the stratosphere).
The 'sweet spot' for MOM according to published sources is indeed 200-240 (some however say higher).But of course (one class) 200-240 is exactly where the A321NEO is.indeed the LR is suggested to carry circa 210 in 2 class.Overall fractionally bigger than a 752 and about the same as a 762.
If you put too many seats into the A321LR you start running into baggage limitations, it is already getting tight with ~200 seats (again on the LR). The A321LR also needs a new wing to move fuel capacity from the cargo bay into the wing freeing up space for bags, in addition to all the other advantages the wing would bring.