Yeah, I try to practice the same, module-after-paycheck, although I cheat a bit with cheap used utilities.
Tricky question! To me the separate VCas are needed as soon as a traditional vco shows up in the rack. And although I use an external mixer for stereo out I quickly found I needed mixer modules as soon as I had more than two sound sources going. I like being able to pan mono voices and/or have a few stereo possibilities as well (esp with Rings, Clouds, Beads…). The Intellijel has stereo out, right? (First time around I just had the niftycase and its weakness is the mono out so I had an in-rack stereo mixer right away).
Maybe a simple dual vca and a little mixer at the same time as soon as you decide on another sound source in the rack? If /when you need to upgrade later they’ll probably still be useful utilities.
But – this is just my way of reasoning, related to how I make my music. There’s no absolute truth :-D