I have a similar bar/half wall situation, but with a granite top instead of butcher block. In my case, I screwed a piece of MDF to the top of the half wall, and the countertop installers then glued the granite to that with a strong adhesive. This works because the granite is doubled at the edges, so the MDF is mostly hidden. If it would be feasible for you to rout the bottom of the butcher block 1/2" deep everywhere except the edges (I'd suggest leaving an inch around the edges full thickness), then you could do pretty much the same thing as me, with a layer of MDF screwed to the wall to provide support for the butcher block.
Make sure that the MDF is installed level - otherwise, when you level the butcher block, you'll have MDF peeking out from under it at one end. Don't ask me how I know...
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
This answer assumes the countertop doesn't have an integral (pre-formed) back splash.
In order to move the countertop back to have the entire edge touching the wall you will need to scribe a line.
To scribe a cut line you must first get a scribe. This is nothing more than a compass, but one leg has a holder for a pencil ( the other leg is pointed).
To use it first orient the countertop so it is square to the cabinet bottoms. Depending where the gap(s) are located you must now find the space furthest from the back edge. This is the distance to set the compass too (the space between the pencil and the pointed leg). Tighten the nut so it remains at this setting.
Be certain to secure the countertop so it doesn't move (clamps or screws). Next, with the pointed leg against the wall and the penciled leg on the countertop angle the compass slightly(so you are pulling it) and pull it from one side of the countertop to the other. Keep both legs against their respective surface.
If all has gone well you should see a pencil line that tapers when compared to the back edge of the countertop. This is your cut line. Removing it will allow the countertop to fully contact the wall.
Check This First If you have a countertop that has a lip or bull-nosed front edge be sure the amount that you need to remove isn't so much that the lip prevents it from touching the wall.