Is the drywall painted? Primed? What size are the tiles?
Is the glass tile clear tile? Is it semi clear?
The TCNA specifies that the glass tile manufacture specify the setting material for glass tile installations. Since your install is not in a wet zone you should be OK but if you have a primed wall and glass tile the mastic may never dry behind the glass and you might develop "ghosting" or mold closer to the stove.
A product like Laticrete's 254R is an excellent thinset for both glass and marble and sets very quick. I would use something like this instead and a very small notched trowel to set the pieces. When installing glass tile often the thin-set can be seen through the glass. You need to press these tiles firmly into the setting material to ensure full coverage on the back or you can see the voids and often the trowel lines if poorly set.
Hope this helps.