I think it mostly boils down to whether or not you want to wait.
Cadets are available now, but Chromagnon and Visionary Series II are still a bit of a ways off. LZX are surely working hard to get them out as soon as possible, but there’s no guarantee yet of when they’ll be out. So if you do decide to wait, and expect to be able to get them when the latest ETA says, there’s a chance you’ll end up having to wait longer than expected if there are production delays. (LZX has been reworking how their products are produced to eliminate as many potential production delays as possible, but you can’t plan for everything.) Any release dates you hear now are estimates, not guarantees. Please remember that, if you decide to wait.
If you do get started with Cadet modules now, they’ll still be able to work with newer modules, especially since one of the upcoming modules is the Sync Distro module that will convert between 14-pin sync and RCA sync (and you can also use Cadet 1 and Cadet 2 to do that right now!). Or if you eventually end up wanting to skip that Sync Distro module and completely rid yourself of 14-pin sync in the future, that would mean Cadets 1, 2, 4, and 9 are out, but Cadets 3, 5, 6, 7, 8, 10 are still fine. (So that’d be 7 module out of the Cadet 21 setup, and the other 14 would potentially still be useful.)
Personally, I think if you enjoy DIY (and the LZX ones are definitely some of the easier ones to build), then you might as well start now with Cadets, and add a Chromagnon and Visionary Series II stuff when it’s convenient for you (after they’re released, of course). The Cadet series is really a great series to start getting the hang of things, and you can still make some pretty cool stuff with it. Plus if you’re interested in figuring out the “how?” behind the electronics or if you want to tweak things, there’s nothing better than Cadets. (If you do go the Cadet route, I highly recommend also picking up a Staircase at some point, since it really helps a system with fewer/simpler oscillators feel beefier.)