Got this macbook for free as a gift from a friend that had just bought a newer one. Honestly, installing Linux was very straightforward. The only hitch is the wifi chipset; it uses a proprietary driver so in my case it was necessary to connect my phone via USB and tether so I could install the kernel module needed for wifi. A non-issue if you've got an Ethernet dongle, or a router that allows USB connections. Other than that, it was no different than installing on any other machine. The cool part is how it boots: the apple bootloader is preserved separate from whatever Linux bootloader you choose (grub, in my case) so the machine boots Linux by default, and when I want to run macOS I just reboot and hold alt(cmd) and select my macOS partition in the macOS bootloader.
As for distribution choice, I settled on Ubuntu for my mac purely for the sake of time. I wanted the hotkeys for keyboard backlight, screen backlight, volume, media keys, etc to work with minimal dicking about, and Ubuntu is the easiest distro to make that happen. The big upside is that the keys all send the standard signal they ought to send (vol up sends the XF86RaiseVolume, etc) so if you do want to use other distros like Arch or Gentoo, it won't take long to create a config file for something like xbindkeys to get them working, and then just add a line to .xinitrc or your window manager config if it allows for launching programs from the config to automatically start xbindkeys. I just prefer having all of that done for me at the system level so it doesn't matter what DE/WM I'm running, it just werks™