It's not a design principle or "rule" but in this case the walls behind the shelving would look better if the blue were continued onto them. The reason has to do with contrast. The white shelves on the cream walls look a bit washed-out. The white shelving upon the blue walls would be quite strike and present a more polished look! Happy painting to you!

I would stick with the alabaster. All of our trim and kitchen cabinets are painted SW Pure White. Definitely looks more cohesive than if I would have changed up the color. The only thing that I would caution is to find out exactly what they plan to use to finish the cabinets. Factory finished cabinets use post catalyzed conversion varnish. Make sure that they prep the cabinets appropriately and use the correct products for a durable finish.

I dont see any reason why not, if thats what you want. I am not so sure that navy and yellow are coastal colors though. You might get by with the navy, if you chose a light aqua beachy color instead of yellow.

From your description I would advise you not to paint the walls white. White needs light to come to life and becomes drab when you don't have enough light. With the flooring you selected I would stick with the taupe colors for your walls. Taupe can be tricky. I have found that many of the taupe colors in both SW and BM tend to either be too gray or have too much purple. The nicest taupe I have found is by C2. You can order samples and paint from the company if you don't have a C2 store in your area. Test the color Filament and Archival. The first BM color I would test would be Pale Oak. It is a bit more gray than the C2 colors, but is a light taupe. I would paint the ceilings the same color as the walls.and would use white for the trim. The white should be the same hue and the white counter. Please test paint colors using large samples. I like to paint my samples on 140 lb watercolor paper - it simulates walls pretty well. Spraying paint creates a slightly lighter color and colors look lighter when they are on a perfectly smooth surface. Most pre-painted samples that you can buy are sprayed and on slick paper. Michaels, Hobby Lobby and Amazon have watercolor paper in a variety of sizes. For neutrals and whites I like the larger sheets (18x24). https://www.amazon.com/gp/product/B00NQ49PLM/ref=ppx_yo_dt_b_asin_title_o08_s01?ie=UTF8&th=1