We actually use the outboard engine on the pilots side to reference the taxiway edge which is how we judge turns and things like that. The hardest thing to do on the ground is a 180 degree turn on a 150’ wide runway (standard width). Most runways have extra paved areas at each end called keyholes which are used for these turns but if a runway doesn’t that 150’ is juuuuuust enough space to make a perfectly executed 180 turn. Of course if you fuck it up you’re stuck there until they get a tug to move you and you’ve shut down the runway for awhile, doesn’t look good.
As for the AR, the vibration is just the natural result of two machines moving so close together at high speeds. The USAF has two tanker’s (currently) and each poses a unique challenge for the C-5. That video is from a KC-135 which is much smaller than the 5 and because of that, FRED tends to push them around really easily so it is very challenging to keep the jet stable and not upset the tanker. The KC-10 is bigger than the KC-135 so doesn’t get pushed around as much but it has a 3rd engine on the tail and that engine fuck with the tail of the C-5 because once you get in contact (the position where the boom can plug) the jetwash out of that 3rd engine pushes on your tail. So there is a significant change in how the C-5 controls once you get in contact and it is very easy to get pushed back out.
I can’t tell if that video is sped up or not but i would say a competent pilot can get from pre-contact (about 50 feet away) to contact (about 10-15 feet) in a few minutes or less. The key is not to be fast but to be smooth and stable. Of course you can’t take so long that you run out of gas just trying to hook up with the tanker so it is a balance.
So much of flying these days is really just programming the autopilot, air refueling is true hands on piloting and requires immense concentration and constant minor adjustments. Twenty minutes on the boom in bad weather and you’ll be completely spent mentally and physically.