Looks pretty good to me. I like the combo of batumi+maths with the MSS, a dense digital modulator and a roomy playable one. I also like having an extra filter.
What are you wanting to use Pam's for? I'd personally drop it in this case, with the MSS I don't like Pam's menu system and ended up just loading WYSIWYG modules around the Moogs, much smoother experience. Pam's reputation for being godlike in small cases is well-deserved though so don't let me stop you. You have a ton of clocking and ways to sync modulation already so she loses some lustre here imo, I'd personally rather have a patchable clock divider when you have so many sequencers, but I'm a Bindubba man so I get on with that kind of thing.
Couple random things come to mind:
-- MN modDemix is a fantastic module to pair with Maths, I love it in small cases. Basic functionality with much more at the right price. If you decide to add a VCA or small mixer, shortlist this one 100%.
-- A smallish EG/LFO is a great supplement to stick next to Maths if it can fit. ALM's Pip Slope mk2 is a favorite in 4hp with much of the same controls as on the main Maths channels.
-- Triple Sloths is another dense modulation powerhouse you could consider, much more hands-off but has the influence circuits so it's not just an island. NLC makes a lot of creative and unique modules, be worth a look through if you're interested in adding some chaos/random.
-- Check out the Turing Machine and brethren out there, could pique your interest. You may be the target audience for Ritual Electronics's Amnis, I love it in this category (shift registers), lots of fun with all the gate outputs especially and only 6hp. These are great for CV modulation, not just sequencing notes and gates.
-- Playable touch controllers like Bela Gliss or MN Press Point. Just fun interfaces that don't take up much room.
-- You may want a source of tuned voltages for transposing, something like a Befaco Voltio, but if you've got a keyboard or something handy to feed into the VCOs then I'd forget it. Especially the SubH really benefits from having a precision adder around, but if you're focusing hard on percussion and rhythm, skippable.
-- The DFAM has had a few 3rd party companions developed to expand its functionality that might greatly interest you. Check out the MAFD (midi adapter for dfam) and DFAM Thing. Grabbing one of these could totally change your approach and what you decide to put in this rack. Seriously this may be all you need to get freshly busy for months with your current setup.
-- With all of your instruments having standalone sequencers on them, maybe something else for the 1U row.
And hey you've got several Moog ladder filters and VCOs already, you can always synthesize your own drum sounds from simple building blocks like Maths. You could also sample them, by far the cheapest way to do modular drums rather than get individual voices. Check out the Squid Salmple which is a monstrous pairing with the MSS.