that flowerhorn will probably destroy the others in a 4ft tank as they can be extremely bad tempered. the 6ft footprint will give you a much better shot at a community if the flowerhorn is non negotiable.
the 4ft footprint is better for less aggro community of cichlids like sevs, jacks, FM etc or one big aggressive fish like a FH or grammodes.
the cuban and FH will probably fight badly, maybe to the death, eventually. 6ft for those 3 bad boys together IMO, even then that may not work. it may be fine now but they are young if your still growing them out. most aggro cichlids dont start getting nasty till they know they can back it up, usually around the 5-6" mark.