There is an easy fix to your coating problem.
Wrap the coater in a layer or two of Kleenex, or toilet tissue. It will help smooth out the coating and eliminating streaks.

Some years ago I did some experimenting with not coating, and also with spraying a variety of materials on the image. The uncoated ones began to change color and solarize after several weeks. The result was not undesirable and a few of these I coated at the point they looked good. I still have some of these.

Those which were spray coated with various products eventually, up to a couple of years later, had the same result. Coating these as they aged did no good and they eventually faded to nothing.