Moss grows darn near everywhere in the PNW. And not just because of soil acidity. Typically, it is a combination of issues primarily relating to lack of fertility, soil compaction, persistantly moist soils, and shade. But it manages to grow pretty well in sun, too :-) The good news is that it is harmless in place and actually makes a pretty decent groundcover, provided the other growing conditions are suited for the desired plantings. IOW, you don't need to remove it unless you want to :-) I'd certainly test the soil before doing any liming - if you are in the 6.0 to 6.5 range, skip the lime.

btw, it is unsual for a west facing garden to receive sunlight so early in the day, especially this far north. Are you sure about that orientation?

When you want to have beds with different pH's it is best to make the one with the greatest difference from the native soil a raised bed. Then you don't need to worry about the native soil affecting the pH in the raised bed. I recommend making one more precaution, and that is placing a layer of gravel under the raised bed. Rhododendrons and azaleas do well in raised beds due to their very shallow roots. They do need a lot of mulch to conserve moisture and keep the roots cool.

I agree that moss is an asset. There is a garden in New Jersey that everyone loves because all of the paths are "paved" with moss. My wife want me to do the same in our yard. Our soil is not quite acidic enough.