I think your instincts about quantity are right on - 2 or 3 (depending on the height of the items to be displayed) feels right for the height of that space. You want to take a close look at the shelf images you posted and compare with your space. It's a little hard to tell without more images of your kitchen, but it looks like you have a "transitional" aesthetic, not quite modern but not quite traditional either. The shelf images you posted are both of very modern decor. The reason the long shelves look good is that they are very thick, and the reason the thick shelves look good is because the aesthetic is very modern. Floating shelves can certainly look good in a transitional setting, but they probably want to be thinner and therefore shorter. In addition, I would keep the layout symmetrical rather than staggered (again, staggered is more modern). Consider either a set of shelves of moderate length centered in the alcove or two sets of shorter shelves each centered over a pair of cabinet doors. If appropriate for the items you plan to display, you might also consider shallow picture ledges like the image below, rather than full depth shelves.

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Most floating shelves need to dig into the studs before the tile goes up. You may be limited to exposed bracket ones now, depending on the weight desired to be placed on it. Some of the “decorative” floating ones barely hold themselves up.