Also using Stellarmate on a RPI4 , have it mounted on top of the telescope with a USB power unit so totally portable . I am using the Flirc case I had to turn it upside down and all my WiFi issues were solved. The RPI4 is a lot faster than the RPI3B I was using.
How did you fit the RTC I used it with some wires and just wrapped it in some tape . Not much room in the Flirc case.
I am using Kstars on a Macbook Pro with MacOS Catalina and works well mostly but does crash when capturing images/video as you have had the same issue. I did report that problem here also. I tried versions 3.4.3 and also an older 3.4.1 still crashes at times when capturing images.
To get around that I run ccdciel for imaging still using Kstars/Ekos for Platesolving and mount control.
I am using ZWO camera, filter wheel and a AZEQ6 mount.