Would be bad to have full authority with the rudder pedals
That's the most important thing. I think it's easier for taxi qualified non-pilots to learn the tiller, easier to feel what you're doing and easier to learn than steering with your feet. It's also a bit like the second driver on the tail end of a ladder truck in that it's very
different than driving a car, but at the same time it's not difficult if you take it slow.
I don't think the invented the modern airliner tiller with that in mind but it certainly doesn't hurt and it makes doing business easier.
This I do not know. However, there is a common problem across the entire (?) E6B fleet that is apparently in need of replacement or failing. I don't know how expensive or difficult it is to fix.
It's a bit of a frankenplane and they only bought a handful of them. It's probably got more in common with the old AWACS and JSTARS airplanes than the KC-135, which is more like a weird cousin of the 707 family. All of them are derived from the
prototype that Tex Johnson rolled... twice and gone through various modifications and derivations.
The P-8 is a frankenplane 737 but at least its production run should give the parts supply some safety in numbers.