Not sure about the washers. I think there's a torque spec for the bolts.
I would did the junk stock shackles in favor of heavy-duty ones. I wore oval holes at each end, and actually broke one.
I don't believe that they had rear bumpers. The spare doesn't count.
Yes, that's normal for the water tank. I had a problem with mine where when I was refilling at a truck stop it actually grew so much that it actually squeezed itself out of the mount. After that I remounted it, but also got a set of ratchet straps to run underneath it. I didn't want it to pop out at an opportune moment (in front of the axles). Not sure it was completely necessary, but I felt more secure with 'em on there.