Hello,
About the speed of SD card, I have got this response from the Elektron Team (Thank You Patrik :)) :
Tonverk implements UHS-I, so there’s no point in choosing higher-spec cards like UHS-II. You should be able to use SD cards of any size as long as the filesystem is exFAT. Our recommendation is to choose a reliable UHS-I card from a known brand, with performance as close as possible to 104 MB/s.