Your signal flow there is correct.
The VCA and Envelops are combined in the Patching Panda Punch and the Befaco Percall, you can build both from DIY kits if you don't mind a bit of soldering, the Punch is a very easy build.
I seem to recall someone on here recommending a https://www.modulargrid.net/e/4ms-company-percussion-interface and https://www.modulargrid.net/e/4ms-company-percussion-interface-expander which they said would like you turn an audio input into a modulation source, might be worth having a look at.
Enjoy your spare HP, don't rush to fill every last space, this is not like filling sticker books. Resist the urge to 'complete' your rack, its never complete so just relax.