You can put it onto the drywall. You want it smooth and to not have a glaze, so you may have to sand it. If its been painted with a topcoat, you may want to paint it again with a primer.
Use mortor that is specifically designed for glass tiles, not ceramic tiles.
Protecting the Cable
National Electrical Code 2014
Article 300 Wiring Methods
I. General Requirements
300.4 Protection Against Physical Damage.
(F) Cables and Raceways Installed in Shallow Grooves. Cable- or raceway-type wiring methods installed in a groove, to be covered by wallboard, siding, paneling, carpeting, or similar finish, shall be protected by 1.6 mm (1/16 in.) thick steel plate, sleeve, or equivalent or by not less than 32-mm (11/4-in.) free space for the full length of the groove in which the cable or raceway is installed.
Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
So you have a couple options.
Free Space
Run the groove deep enough, so that there's 1 1/4" of free space in front of the cable.
Steel Protection
Protect the cable using a 1/16" steel plate, or sleeve. Or install the cable in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
Dividing the Circuits
National Electrical Code 2014
Article 210 Branch Circuits
I. General Provisions
210.11 Branch Circuits Required.
(C) Dwelling Units.
(1) Small-Appliance Branch Circuits. In addition to the number of branch circuits required by other parts of this section, two or more 20-ampere small-appliance branch circuits shall be provided for all receptacle outlets specified by 210.52(B).
III. Required Outlets
210.52 Dwelling Unit Receptacle Outlets.
(B) Small Appliances.
(1) Receptacle Outlets Served. In the kitchen, pantry, breakfast room, dining room, or similar area of a dwelling unit, the two or more 20-ampere small-appliance branch circuits required by 210.11(C)(1) shall serve all wall and floor receptacle outlets covered by 210.52(A), all countertop outlets covered by 210.52(C), and receptacle outlets for refrigeration equipment.
Exception No. 2: The receptacle outlet for refrigeration equipment shall be permitted to be supplied from an individual branch circuit rated 15 amperes or greater.
(2) No Other Outlets. The two or more small-appliance branch circuits specified in 210.52(B)(1) shall have no other outlets.
Exception No. 2: Receptacles installed to provide power for supplemental equipment and lighting on gas-fired ranges, ovens, or counter-mounted cooking units.
So as far as your plan for dividing up the circuits, you're spot on.
Best Answer
Yes, if the wire is out of service, remove the plastic panel, secure the wire with insulation tape and put your tile over it.
"Out of service" not connected to the main telephone system!
If it connected, but you have other PSTN jacks in the house, cut the wire ONE by ONE with insulated wire cutters!. Then insulate each wire with tape and finally the entire wire.
You will also need to remove the socket on the right, and then replace it when you done tiling, as the mounts need to sit ONTOP of the tile, and the plastic cover will hide the mounts nice and flush.
You could also leave a nice message for somebody in the telephone box, when they take the tiles down in 25 years, that it was a telephone wire.. or where you buried your gold treasure. Heheheh