1-Usually that is just the zinc galvanizing and it will flake off all by itself, not usually a big deal. The tension is supposed to be snug without any tension. It will relax a bit now that it is assembled but only tighten it if it needs it.
2-don’t worry about the washers those are for the old configuration. The resistor goes on the t0 terminal unless you have an extruder. This is shown on the ramps page of the assembly instructions.