We're flying IB intra-Europe and transatlantic and wondering about J seats:

MD-87: An A-C pair seems best to give us some extra space, rather than taking a DF pair. Any better or worse rows?

A320-100/200. They don't seem to block the center seats. Is this correct? All of row 3 is currently taken for one flight, which seems odd for a November trip.

A340-600. We now have 2AC and row 1 is taken. Would 6AC or JL be better?

Will we have any problems bringing a standard US size rollerboard on board any of these flights?

thanks