Quick note: I finally tested the 3B+ I got recently and its root hub is Multi-TT like the 3B V1.2 (“non-plus”). This means it can support 4 FCDs plugged directly into the rPi and in general it’s easier to get many FCDs to work than an rPi4B. I would thus recommend ordering 3B’s over 4B’s… Digikey has them in stock as do other rPi distributors.
I updated my older posts that have more detailed info: FUNcube sample rate dropping and disconnecting - FIXED - #3 by TvE and the one just before it in the same thread.