Good questions. The answers are on FT, though you really have to dig to find the info.

Let me answer:
By default, conversation between the middles seats will be difficult, however the J seats can "move" forward in upright seating position for around 10-15 cm, makes the situation to speak much easier, though it's still not "side-by-side" or "holding hands". Reverse herringbone seats are super, though have some disadvantages and this is one (another one, for example, being it difficult to support a child over the seat barrier).

The foot wells are all equal size, or at least nearly equal that it would need a stick to find the differences, though the first row in the second cabin is shaped a little different. This YT video shows (at the near end), how it looks: . I would not say "it's bigger", to the upper side even more limiting, I would say.

The first middle row in the J cabins do have a smaller/lower "divider" between the seats in the foot well area as well no screen-holder intruding. It's more or less "possible" to step over the divider, whereas you can not do for the other seat combinations (that would be "climbing").

Another item to consider is the "bending your knees" area. The A/G seats do give a lot of room to bent your knees, when sleeping left sideways. The D/K seats do so, when sleeping right sideways. Being nearly 2 m tall, I do think, you would fit in top to bottom, when laying down on the back, head touching, etc. So, the sideways sleeping items might be important to consider for you. The quoted video shows this aspect to.

The first middle rows in the J cabin give the D seats some more space to the left side and the G seats to the right side, not super, but it's there.

The 11D/G are by far the worse J seat locations due to the toilet and general aisle intrusion, though it is still significantly better than anything Y or even PE, especially those Y/PE seats that are "on the aisle side seat block corners" or near the toilets. When seated in 11D/G, speaking with the ISM (In-flight Service Manager) and asking her, she encourages the cabin crew to keep the curtain properly shut, can help very much to avoid disturbance. Some ISMs are, without asking, very strict with that, though there are also some, who are relaxed about that. The ISM is the cabin attendant with the gold jacket (though I also have seen them sometimes wearing a black jacket).