I would extend the size to meet the control joint because leaving a 2 inch wide strip between your new concrete and the joint will make it crack at the corners. So make your cutout 36” x 38”. A 4’x4’ box is way overkill. They recommend rebar in the new concrete. It wouldn’t hurt and then you won’t be worried about it if you add it. Use 2 bars each way. You can even tie them into your new pins to keep them evenly spaced. Your drawings look good with the one mod to extend to the control joint. You don’t need vertical rebars.
Also, use the highest strength concrete you can buy (close to 5,000 psi?). Mix it using the least amount of water possible, because mixing it with more water makes it weaker than the mix design strength. Vibrate it if you can while placing it, but if you don’t have access to a vibrator, you can tamp it down to ensure it fills all voids.
