Hi, if I can give you a little bit of advice: head over to the Linux section of the forum- you will surely get help there.
https://forum.cockos.com/forumdisplay.php?f=52
As for my own experience, I tried jack+Carla but only had headaches with it on Ubuntu.
Two things I changed were I use ALSA instead of jack, much simpler to use and I installed Lin VST which is a more transparent VST wrapper for Windows plugins in Linux. Yabridge is a popular one on the forum at the moment and is getting a lot of love. I haven't actually tried it myself yet.
If you really need to use Jack+Carla for some reason, then let the folks there know why and I'm sure you'll get the help you need.
Good luck.