Not much tweaking of NixOS itself was needed. But we currently cannot automate the firmware setup, so this must be done by hand.
=== Before installation ===
These settings are needed both for booting the final install, and installer itself. Therefore, they must be done first.
* ''Disable Secure Boot (but keep UEFI Boot).'' Thakfully doing so is as easy as changing any other simple setting.
* ''Disable Intel hardware RAID and use AHCI instead.'' Intel doesn't seem to provide a working linux driver for this. (If you just have SSD it's pointless and just slows things down needlessly anyways.)
~~Wifi does not work with kernels older than 5.1 (firmware not present) or newer~~ (https://bbs.archlinux.org/viewtopic.php?id=247705)
Update: The 48.ucode causes the Killer wifi card to crash. The iwlfwifi-cc-a0-46.ucode works perfectly. default.nix contains an overlay that removes the offending ucode from the linux-firmware bundle.