If you go P3 You only have to design the back third of the play field with the front 2/3 taken care of by the platform. It’s a quick way to get going particularly for someone strong and software and can leverage the unique features of the P3.

You have a large wish list for elements you would like to put in the game. I would put prioritizing this part of the design front and center and work your theme around what’s fun to hit and within your skills to build. If you are going with a traditional machine format, the first decision will be the playfield and cabinet width. Will you be cannibalizing another machine for the cabinet? If so, that sets your width. Generally, widebody machines tend to have a slower feel to the game, although active elements in the lower play field or an increased slope can change that. An early decision will be how many ball paths will lead from the mid playfield to the upper play field. I’ve found that paths less than 1.5x ball width are very difficult to hit and 2x width a practical minimum for my playing skill. Between each ball path will need to be a post or target which also gobbles up width. These will be primary constraints on your geometry. One thought I have about the theme, the blocky pyramid Architecture is at odds with the sloping nature of pinball ramps. To me, this calls out for an upper play field being the top of a pyramid (or plaza) with a ramp hidden on the side. Pops can be trees and jungle. A toy that drops into the mid playfield ghost busters style gains you a removable target. These are just ideas worth what you paid for them. Oh, how are you controlling? Multimorphic, FAST or cobra? MPF?

I used multimorphic boards on my home brew, my current project and plan to for my next one in the early design stage. I like that board set because it is well supported in Skeleton Game and MPF with native support for steppers and servos. Very robust.