Looks like the issue was a broken USB stick. I used a different one with sudo dd if=Qubes-R4.1.1-x86_64.iso of=/dev/xvdj status=progress bs=1048576 conv=fsync and that just worked.
I managed to install 5.18.16-1.fc32.qubes.x86_64 in dom0 through USB tethering with an Android phone, and after rebooting I ran the Qubes updater which gave me 5.15.64-1.fc32 for sys-net.
After that, everything seems to work without any additional tweaking: audio, suspend, even the touchscreen. Overall, I’m very pleasantly surprised! 
Thanks for your help!