CV Tools isn't a bad way to work, really. Since it's an Ableton plug in an Ableton DAW, the integration should be very easy with the ES-9.
But as for that rack...yep, go bigger. The REAL thing you want here is FX processing with what would essentially be the entire modulation section of a proper build, and that's not going to fit this "beauty case". But make sure to use this build for, as plragde notes, FX that your DAW can't exactly do with the same level of control you'll get manually with a FX build. One other change I'd recommend would be a much beefier power supply, since your build lives or dies depending on whether you get a hefty enough P/S. Always overspec the supply due to inrush currents; if your +12v rail has 1500 mA on it, you want a 2000 mA capacity on that rail. Go at least 25% higher in amperage than you appear to require, as most any circuit has a degree of inrush on power-up. It only lasts a few milliseconds, but it IS enough to pop the supply and shut down the rig in that tiny sliver of time.
Oh yeah thanks for the heads up. Hadn’t realized the margins in power is probably wise.