The drop distance depends on the trailer height that you will be using.
You want your trailer to sit/ride close to level when loaded especially a double axle hauler. You want the trailer to carry the weight and the bus just push,pull and stop.
You can always add clips to the bumper for the ramp and or steps.
Adjustable hitches are nice when switching between different trailers or attachments.
You can make your own with channel iron attached to your square tubing.
Last time I built one I used a apiece of 3" channel welded to the slide in and a piece of 4" with with the ball attachment weld to it with corresponding holes up and down the 3" and holes in the 4" just over the ball and just under the ball for 3/4 grade 8 bolts