You need at least the additional 1/2" of BCX grade ply, 3/4" would be better, then the 1/4" cement board. No CDX ply, the "D" layers have too many voids and the sheet carries only a sheathing rating from the APA, you need one with an underlayment rating.

Apply a paint on waterproofing around the edges of the ply at the sink cutout and extend the coverage on the surface of the ply for about 6". I also paint the underside of the ply above the dishwasher to give extra protection from high humidity buildup there.

Set the cement board in a bed of thinset and anchor with 1 & 1/4" galvanized roofing nails, then tape the seams with fiberglass mesh tape and a coat of white modified thinset.

How do you plan to finish the facing edge of the countertop?

Thanks tileguybob! I never thought about the waterproofing! So I assume your saying that I should go with the 3/4" ply, 1/2" ply & the 1/4 cement board(backerboard)?

I will be using a wood nosing (maple) on the front edge.

Should the tiles butt against each other when installed?

great advice bob.

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Do not butt the tiles, leave at least a 1/16" grout joint. No matter how tight you think they are there is still enough room for food particles and dirt to get in there and turn to mold and bacteria. Just applying grout over this condition does not give the grout enough room to bite and hold, it isn't much more than the equivalent of a layer of paint, which will chip out over time.

Yes, 3/4" then another 3/4" ( 1/2" is rolling the dice in my opinion) then the 1/4" cement board, and it must be embedded in thinset.

One of the last countertops I did, the wood trim was recessed down about 1/4" below the surface of the granite so the top could be wiped clean with no crumbs or liquids held against the wood trim. This meant I had to polish the edge of the granite, which I have the tools to do so and they are expensive. You might be able to use a palm sander and varous grits of sandpaper to get a somewhat polished edge.

THANKS, Flooringworld