C is about the most common choice these days but you could in theory use anything. Heck, write your own language while you're at it. Just remember that you're inevitably going to have to work your way all the way down to machine language/assembly for the really-low level things. (Like bootstrapping.)
Whatever the case, a 68k Macintosh would be a rather bad hardware platform to choose as your first every operating system project. Apple tended to use arcane hardware designs and poorly document them, since they never anticipated anyone really caring to access it outside of MacOS. It's notable that last I checked no one had actually written a "cold metal" bootstrap for BSD or Linux on the Macintosh. Booting them requires MacOS to initialize the hardware before passing control to the kernel via a bootloader that's actually a Mac program. Heck, even A/UX boots that way.
Of course, I seriously doubt this challenge is *serious*....
Whatever the case, a 68k Macintosh would be a rather bad hardware platform to choose as your first every operating system project. Apple tended to use arcane hardware designs and poorly document them, since they never anticipated anyone really caring to access it outside of MacOS. It's notable that last I checked no one had actually written a "cold metal" bootstrap for BSD or Linux on the Macintosh. Booting them requires MacOS to initialize the hardware before passing control to the kernel via a bootloader that's actually a Mac program. Heck, even A/UX boots that way.
Of course, I seriously doubt this challenge is *serious*....