I'm not a professional painter. However, I have some experience painting, and have read a lot over the years. If a wall (especially an exterior one) has never been painted, two coats over a primer is probably a good idea. Two coats is, IMO, a requirement if the paint is being sprayed on. Some will likely disagree with this, but sprayed-on paint looks thin to me.

Painting over bright or dark colors can be a challenge, and may require up to two coats of primer before the new paint goes on. Provided the walls are clean, most light-toned colors are easily painted over, so you only need one coat. If walls aren't clean two coats of paint may not make a difference.

depends on the paint and the previous layer... you may be able to get away with one coat but in my experience 2 coats is necessary for full, rich colour coverage.

I get the primer tinted the same color as the paint . Then you only need one coat of primer and one coat of paint.

I like two coats of paint. It seems, it deepens the color a bit more and just looks nicer.