Stages and Maths would be OK normally, but the Akemie's is going to eat envelopes for breakfast. Remember: Chowning FM is very envelope-intensive...that's how you get your timbral shifts within the duration of an event, by applying multistage envelopes to a lot of the oodles of parameters. If I were you, I'd be looking at a couple of modules that have a lot of envelope generator density, such as Qu-bit's Contour, Doepfer's A-143-2, or a combo of Erogenous Tones' RADAR and Ping. That'd really make the FM pop and jump. Plus, yes, do consider a basic VCF for the Akemie's...the combo of FM + good analog filtering is something you'll really get fond of.
Also, I'd lose the Roland mixer. For one thing, it has its own 1/4" out pair, and your Intellijel cab has that already (plus you also have the Intelljel I/O in the build) and having another pair of outs seems redundant. My take there would be to go smaller, but still stay in stereo. Have a peek at Verbos' Scan & Pan...stereo, four in, VCA level control plus CVable panning, plus some neat capabilities for crossfade/channel scanning that are a bit unusual, all in 14 hp. That also solves your VCA question, given that that mixer can do your exponential audio VCA duties, leaving the Quad VCA free for CVs or other spot applications where a single free VCA is needed.
Hmm...that Basimilus...do you need it? You could jam a couple of Moffenzeef Dial-ups in that space and still have 2 hp left...or, you could reclaim a bit more space and add those plus a Muskrat for three channels of glitch/noise percussives. Or the Dial-ups and maybe a couple of Erica Pico Drums to combine conventional sampled drums with glitched-out ones. So, instead of going with the question of adding a filter for a single percussion source, see if you think that a few of them minus a filter might be more capable. That would require more gate/trig channels than the Metropolis would have, but since you're contemplating the Varigate 8+ already and that one would be more than ample, I'd say go with that instead.
Last, swap the buffered mult for Intellijel's passive one. You're not splitting CVs enough in here to worry about voltage 'sag', so regenerating CVs won't be necessary, and you can save a few bucks that way.