Thanks for the feedback.
The size is temporary; I figured I would start small, get a feel for things and not get too overwhelmed. As of now, I have just an 84HP panel. I do intend to expand to something a little larger, or add another 84HP panel. When I do, it will likely consist of more control/modulation modules, perhaps another voice or two, as you suggested.
I'll have to check out Time's Arrow.
Maths is definitely a module I am considering, pairing it with various logic as you suggested sounds pretty interesting.
Are there modules with quantizers and shift registers? I know there are plenty of logic functions out there. I am definitely not against making some myself as well; would be a really good use for the random IC's I have floating around in drawers.