Couple of things...first, lose the mults. This build is too small in scale to lose 6 hp to modules that should REALLY be replaced with inline mults and/or stackcables. Plus, you really don't need a buffered mult unless you're trying to split out a scaled CV to 4+ devices, as you'd need the buffering to mitigate voltage sag that can happen from this. But if you've only got two or three audio generators that (might) need this, the buffering is superfluous.
The other thing is the drum modules. I'm not sure if it's been said too much, but I'm going to say it again here: modular synths really aren't drum machines. You CAN build one, of course...but you'll only find a couple of advantages to it versus a proper drum machine, which is a mission-specific device that's designed for drum sounds and patterns. In fact, you could easily clock a drum machine off of a Pam's output; you don't have to keep the modular's signals only in the modular.
But looking at this as cost-vs-usability, the idea fails. Right now, your drum modules ALONE are going to run $1055. And you've only got Pam's as something of a sequencing source, instead of a proper trigger sequencer that allows you to write and SAVE patterns. And that module will probably run about $300 and up. Very up, in fact.
OTOH, the RD-8mkii sitting next to me cost $329. Yeah, I know...Uli's a trolling nutjob, and his behavior is sus at best. But it DOES have the 808 soundset (and it's very convincing) along with a few classic Boss DR-110 electro noises and a very familiar UI. I just cringe, get over it, and keep on going, actually, and the RD-8 (plus a pair of RD-6s...I'm recreating an OLD setup from before 1995 that I found incredibly effective at the time) ticks right along. I can lock it up on sync from a number of devices, ranging from Beatstep Pros to the DAW via my Antelope Orion 32, too. True, some people won't buy Behringer...for very well-grounded reasons, actually...but I don't have the $10k necessary for the vintage Rolands or a couple thou for the present models, and their "circuit modeling" in their new machines really saps the punch out of their sound across the board, not just with the drum machines.