The minimalist design also leaves only a vague sense of tone. This can be a positive thing, for a play group the has a clear idea of the kind of story they want to tell, and just needs a structured framework to build on.
But a more well-defined aesthetic could nudge a less-experienced group towards a specific mood or vibe.
Given the subject matter, my gut instinct would be one of two trope-y approaches: the “Ghibli way” (or possibly the “Gaiman way”)—emphasis on mood and atmosphere to weave mundane concerns into a spiritual/existential realm, and vice versa—or alternatively, the “Pixar way”—humanize the abstract, and hope it all seems internally consistent enough.
And yes, I realize that neither of these is mutually exclusive.