Easy one first: the galvos protector has protective plastic film on both sides, which must be removed prior to use. And, yes, you should use it.
The galvo calibration, e.g elliptical shape can be adjusted out with settings. However, making sure that your printer delivered the correct size and shape of test pattern will save a lot of grief. Pictures of the pattern are helpful.
As for the apparently higher than expected z-reset, pictures would help. Particularly of the platform, the z-mechanism, and the z-follower trolley. Xheck that the frame is square on a known flat surface. And also check the installation of the Z-Stop at the top of frame.
The Moai can deliver high-precision prints, but it must be set-up and calibrated. And it takes time.
Layer lines are normal in all additive printing. The resolution used is important. What were the printed resolution of the rings? The closed holes, if not due to inadequate cleaning, are probably related to the Z-axis calibration and, possibly, heating.
As for the pistol grip, resin shrinks. Without knowing more about the model and the axes of dimensional error, it is hard to determine what caused the issue. However, printing directly on the plate will compress the first couple of layers.