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I guessing there is a optimum Nozzle size to layer height vs steps per mm ratio. So how do we figure out?

I'm not sure how steps per mm relates to the equation, but nozzle diameter and layer height are definitely related. You can go as thin as you want, but I wouldn't go thicker than about 75% of your nozzle diameter for layer height. You can, but you'll end up with deeper ridges between your layers.

I've always been happy with .2mm layers and a .4 or .5mm nozzle, but if I'm in a hurry a .3mm layer turns out pretty ok. Much higher than that, and you really should switch to a larger nozzle and increase everything.

I'm wondering if there is a micro step/extrapolated layer height that is less desirable than say for lack of a better term prime height. Should all heights be divisible by our steeps per mm so as to be "native"?

You're not thinking fourth dimensionally

Every straight line move on a delta machine is a triangulation of all 3 motors moving at the same time. It's more complicated than just microstepping the Z up, it's a function of all 3 motors' positions, and the positional resolution of the hotend varies from the center to the perimeter.