Well, you'll also need to replace the Clouds unless you have one on hand, since it was discontinued quite some time ago by Mutable Instruments. Several companies do smaller versions of this; you might look at Michigan Synth Works' Monsoon as a suitable replacement. As for the VCA count, no, six in a build like this...especially for music that has slow, gradual changes such as ambient...seems just fine. But if you insist on keeping this as 2 x 60 hp, you might want to lose all of the 2hp modules and then go with an Intellijel Quad VCA to handle audio, as this also lets you replace the mixer in the top row. And for CV/mod linear VCAs, a Happy Nerding 3x VCA would be a good choice, also allowing summing of CV/mod signals. Which brings this to seven VCAs, but you'll notice I'm not saying that's a problem!
Envelope generator...well, yes, you want that. Actually, more like "need," as that's essential to shaping the VCA and VCF behavior on each trigger from a note. Given the space limitations, you might consider Hikari's new Triple AD, which not only has a summing bus to all three of its AR generators for triggers, but each AR envelope can cycle, potentially adding three more continuous modulation sources to the build.
Last, an Optodist replacement...Antimatter Audio's Crossfold has a number of improvements over the Optodist in that you can literally "crossfold" two incoming waveforms, as well as have CV control over all of the wavefolding parameters. FYI, wavefolding works a bit better here, as you can be more subtle with timbral changes...and in ambient, "subtle" is important.