What screws to affix TV mount to wooden stud partition?
The screws that is supplied with the mount are rated to do the job, the plywood layer under the drywall is the only additional layer that is not typical in woof frame construction. With that in mind, it is still thin enough so the screws will hold the TV you have, or any other TV. The rule of thumb I use is 1" of screw into the framing behind the drywall and the plywood. Your screws you have should give about 1 1/4" of depth into the framing.
Get at least 4 screws into the wall and you will be fine. The shear strength of the screws far exceed the 70 lbs you will apply on them. IMHO....