You should always do two coats for the following reasons:
-Uniform color - if you only do one coat there is no guarantee that the color will be uniform if the previous color is showing through due to improper film build.
-When doing a color change you should definitely not rely on one coat, depending on what you’re changing to, 2 coats is usually enough.

Priming is necessary when you have new drywall/drywall mud to seal it so that it doesn’t absorb more paint than is needed. Also if doing a color change from dark to light 1 coat of primer might be recommended in order to achieve the desired color.

The re-coat window is necessary to ensure that your 2nd coat doesn’t re-wet the first coat. Applying paint too early can just re-activate the previously applied coat of paint, meaning that you don’t get a proper two coat film build, and so it doesn’t cover as two proper coats.

Most paints require 28 days to full harden and cure, giving you maximum durability for the product. only ever wash your walls with warm soapy water, avoiding bleach or ammonia based cleaning products.