Generally, the bottom course should get an aluminum Z flashing starting behind the plywood, then out and over the edge of the brick. The plywood should be brought out to a point where you have enough depth to get backer rod and caulk on all 4 sides where the plywood meets the brick heads.. The depth of the joint should be half the width after the backer rod. Ideally, the siding ( on top of the plywood) should finish up close to the face of the brick. If there is a window on the top side, extra attention on the sill, or even a flashing under the sill may be a good idea. Poly caulk is a good choice.