The majority of the LFO, VCA, and other "necessary" modules are provided digitally via the *ES-9 interface (VCV/Softube/Reaktor 6/Reason/Air/Madrona/Bazile/Buchla/Voltage/Kilohearts/DAW) on all my builds.
All of your Moogs are already in powered cabs. And the Moog 3-tier accessory will work just fine at assembling those into a single unit. So it makes no sense whatsoever to decase the Moogs and reload them into Arturia RackBrute cabs. It might SEEM "convenient", but the real truth here is that you're contemplating spending a lot of money with little return.
A far smarter move...and certainly CHEAPER...would be to keep the Moogs in their cabs, use the 3-tier bracket there, then add something like a Tiptop Mantis at the very base of the Moog rig so that you can have your additional modules there. Even though a Mantis costs $335 street, when you add up the cost of the additional Arturia cases, the cost of the unused Moog cabs, and the extra Arturia P/Ss, this definitely exceeds the cost of the Mantis by a sizable chunk.
One other point, also...what the Moogs need isn't so much additional expensive modules, but more akin to UNsexy stuff...attenuators, logic, a clock manipulation setup to really make their sequencers go nuts, additional utilities of that sort. Sure, some FX and the MScales are definitely called for here. But if you do this RIGHT, with a PROPER additional cab, you'll then have plenty of cheap room in which to build up a more comprehensive "sidecar" for the Moogs than you have currently. Plus, you could just as easily add a fourth "voice" in the additional cab.
The build is already completed and working. Moreover, I simply do not have room for multiple powered cabs. So my builds are designed around an upgrade path of only space for one combined rack/cab at a time as space in my studio is severely limited due to other instruments and hardware (see the "starter rack" image link under the video). And, I've spent years acquiring a rather massive digital arsenal from every modular type software available from VCV, Softube to Reaktor, and everything in between, so I have all of the un-sexy stuff in abundance. And as I mentioned in the OP, I have a taste for Moog and tube, roughly aiming for stuff that is not easy to model - ergo real tubes and such. So my hardware is probably not what someone looking to build a working rack would do, even though it is a perfectly working rack, you just have to account for the digital modules.
I went with the Rackbrutes because I had to have the extra space for the ES-9 as the whole point of going with hardware finally was that it had to work with my digital collection, the leftover HP was just a bonus to grab a few tube modules and space to change them out with others as acquired or needed.
I also had an extra industrial drawer that I could convert into a stand that fit the RackBrutes perfectly, taking up very little space and I can also use it to store modules, cables, and parts in as I acquire them to build the next expansion, and as an added bonus I converted the top drawer into a shelf for the Keystep. The final form or upgrade I have planned is in fact into a 2X2 mantis setup (it's also in my command center as is the intermediate builds) for when I exchange the larger stand that my current monster PC is using with the smaller drawer stand and build a new mid-tower to fit it- again do to available space.
I also have plans to pass the Rackbrutes down to friends or family once I reach the end, so the cost really is not a concern. But I thank you for the sound advice, If I was a sane person it would be most helpful.