> 9. Launch vim, which immediately crashes with error: Vim: Caught deadly signal ABRT

Had the same problem. There's something about this in the FAQ: One should delete and re-install python if it was installed through brew. (Doing this and recompiling YCM worked for me.)

The other gripe was: "Add YCM to vundle" ... without any mention of what exactly to add.

Then the thing started complaining about the missing .extra_ycm_something.py ...