Runit works well enough for me; I've only added one nonstandard service (launch a custom tool to drive an external stats display) and it works fine. My ,xsession has to load some polkit and pulseaudio stuff but that could be because I'm not using a full desktop like KDE/GNOME/XFCE that do those things for you.''

I don't really try to do custom package recipes because I tend to ./configure;make;make install stuff I want at random.

EFI boot is no problem. I think my root is btrfs, but the /boot/efi is vfat. Refind is pretty first-class, but sometimes it has stupid conditions where it tries to default to the wrong kernel version if you have multiples installed (I think it sorts by timestamps or filenames in a way that sometimes work counterintuitively; discarding old kernels largely fixes it)

Haven't really had too many showstopper problems with xbps. I probably sledgehammer it a bit-- occasionally when it says a repo certificate is out of date, I usually end up doing a full update rather than selectively upgrading packages.