Joesh, a few comments:
-- I agree with Lugia, if you have space and $s for a larger case, why not leave yourself some expansion room? That said, Cangore recently put up a very nice small build (https://www.modulargrid.net/e/forum/posts/index/10432); yes it can be done.
-- PNW, Stages, Quad VCA, I have those, those are great. PNW is so good I'd recommend it almost without restriction. Stages is great also BUT since it is so flexible it takes some time and work to understand; I have DATA which helps a lot, I can run Stages into DATA to really see what the envelope is doing as I tweak stages. The Divkid video on Stages is also a big help. I would take Stages over Maths in a smaller build, but that's just me, I use Stages more than Maths. BTW the Loopop video on Maths is excellent, dispels a lot of the "wtf is this" questions. Aside from Maths, you could consider Joranalogue Contour 1.
-- you mentioned you have some external gear (sequencer) etc you would use with the new Modular setup. I would encourage you (if you haven't already) to fully think through how you link and synchronize those. It's very doable; it'll just save you some headaches
-- so much stuff is stocked out lately, I tend to go with options I like that are also in stock vs. waiting forever for a particular module to be available, who knows when it will?
Hope this helps!
Nicholas