Why do you want to do something and not already know how it will look?

Have you searched for images?

Are these stock or custom cabinets?

A standard 42" cabinet will probably be much cheaper than stacked.

16,5" to 18" is usual between the counter and uppers. You have 21.

Your math isn't mathing. You have 54" of "cabinet" space with the cabinets mounted at the standard 54" AFF. If you aren't using custom, one of those needs to be 3" taller. And you need to consider if you want glass, or glass plus muntins in them, because nothing is worse than squat little cabinets with weird horizontal looking panes of glass because that's the only way to do it with muntins and short cabinets.

• 9' x 12"/foot = 108" - 36" (counter height) - 18" (counter-to-cabinet space) = 54"
• 30" + 15" + 6" = 51" so cabinets wouldn't reach the ceiling.

Perhaps a better solution would be to use a slim deco strip at the top as shown in these IKEA kitchen photos, rather than trying to fill the wall to the ceiling: