They're OK, sure...although I think the choice of the Brains module would be better-fit by using the actual Plaits oscillator that Uli ripped off. Costs more, but it's a more ethical choice. As for the FX modules, it's a decent complement, but you might also look at some smaller modules with more capabilities (the FX Aid XL comes to mind here) as keeping things small but playable is one of the keys to making this work. This will involve going to smaller modules, but at the same time you want to establish a point at which things get TOO dense for playability to work for your methods.
Another possibility would be to go with a complex oscillator, something a bit more Buchla-ish. With many of these, you get a continuum of variable timbres instead of the fixed wavetables of the Plaits. Bigger, yep, and more expensive...but more versatile in terms of the timbral variety. You also don't necessarily need a second oscillator for detuning and FM with one of those, since the "second oscillator" is already part of the module.
And while working out the build, try and aim for modules that offer multiple functions. For instance, while it's possible to get separate VCAs in modules, you want VCA modules that can also mix, preferably with a "breakable" mixbus like the Veils or Intellijel's Quad VCA. Or if you want something that distorts, look for devices that get tagged as "character" mixers, etc, that let you submix signals while, at the same time, offering a distortion/waveshaping capability. That sort of thing also helps economize space in a small cab such as the Rackbrute 6U.