Install cyanogenmod on an S5 mini (G800F)
3rd-party recovery is necessary.
Yes.
XDA-Developers also have you covered. You already have the ROM there, why not take some more time to look around and grab TWRP 3.0.0 (newer than provided in your link)?
*.md5 allows Odin/Heimdall to verify image integrity before loading it. It's just your regular *.tar with MD5 attached to it. Odin does not accept *.imgs.


Also, in case you didn't notice, CyanogenMod 13 is available for this device too.