If you install glass tile with mastic, we will have to send the "Tile Police".
Is there even a mastic that anyone claims would work?
Same if you install 1/4" CBU over wallboard. !/4" is not stiff enough because it can only be fastened on 16" o.c. It will flex. Plus how will you finish the exposed board where the tiles end?
Obviously this is a dry area (?), so you can install over regular wallboard once the paper and paste is removed. Otherwise remove the wallboard and install 1/2" backer, then tile just a bit higher past the seam.
The blade advice is good though.