If you really want to do outboard mixing, you don't necessarily need a whole lot of VCAs as was being suggested here.. that'd be a horrendous waste of useful VCAs in your limited rack IMO. Especially when you can just use passive attenuators to turn the levels down from your 10V modular to ~1V mixer levels.
Look into getting some attenuator adaptor cables like this:
https://www.perfectcircuit.com/koma-elektronik-attenuator-cable-5-pk.html
The attenuator is built into the cable so you don't have to use any rack space to go from your modules straight to the mixer.
Or if you don't want a bunch of dongles, then you can use a module like the Levit8 that would have many attenuators packed in a small space. There are quite a lot of options for you to consider.
I do all my mixing in-rack, however, as I like how streamlined that is. But this is also the most expensive possible option.