That configuration he has is 2, 3, or 4 bike.
(You can take the last two carriers off. )
I have 4 trays also. Usually only use 2.
Correct. I have the double bike rack and 2 add-on pieces. Each add-on piece extends the rack by 1 more bike, and most of time I leave it in the 3-bike configuration since that's what I'm mostly using. I bought all of the pieces to make the 4-bike setup for those days when the entire family goes riding somewhere. The pictures I took above with the 4-rack setup was the first day I got everything and I wanted to see how it all looked. Yes it's long, but not much longer than other 4-bike racks out there. Plus each bike platform on the 1Up rack steps up higher than the one it's connected to, so the weight distribution is actually different on the tow hitch than if you had a flat 4-bike platform rack.
However in hindsight, I probably could've just bought the Super Duty single rack and used the 2 add-ons for a max of 3 bikes since that's what I'm mainly using (wife likes using her folding bike that fits in the back of the truck instead of her Super73 Z1). I now have a Super Duty Single rack on order right now so I can use that on my Model Y when I want to mtb'ing with friends or by myself out in the hills.