You’re too kind, but I’m no expert!
I have run 2 transceivers (1 VHF on FLDIGI and 1 HF on JS8Call) with a Pi3B+, each with its own digirig. It was very slow, so I returned back to separate computers for each. But, it can be done. I’ve also made this work on the Inovato Quadra, too.
As far as setting the sound card order, this is a problem, as Linux seems to set them in semi-random order at startup. You can set the order that different sound cards load in, but I have not found a way to isolate and number multiple USB sound cards. I assume this would take some programming that is way over my head.
I’ve found that, if I force the loading order of the HDMI and AV jack on RPi, then the USB sound cards will usually fall into place in the same order as your original setup each time. Typically when they load in the wrong order, its after an update. Rebooting has solved this each of the rare times this has happened to me. I run my portable bag off a Pi 3B+ using a digirig and a USB speaker, both of which are viewed by the system as snd_usb_audio. The last time those cards flopped on me was probably over 8 months ago.