You have very specific goals. Unfortunately, laser doesn’t provide such specific results. Your hair is very dense and coarse on your arms, and you will get a great reduction from LHR if you do it properly with a good laser and settings. However, no one can predict the length of the final hair for you. Patchiness depends on your tech and whether they overlap well. But I can tell you it will definitely look much better if you’re looking for a less hairy look. Generally, hair gets more sparse and less coarse.
Faces are hard to treat. You need a very experienced tech who overlaps well to avoid patchy results.