I like mine on a 8X8X16 concrete block with a 2X4 across the bottom board to set on the block.
I did the same, I'm going to change over to 4x4's. I don't like the amount of sag the 2x4's have developed.
I did the same thing. I found that adding another block in the middle of the run prevented any sag. As to distance apart, that's your call anything will work. I did find that when then hives get closer together, it seemed helpful to make the fronts of the hive look different like painting each landing board a different color. I was told it helped to prevent drifting. As to which way to face them, east, southeast if possible & provide some sort of wind break to protect them.