Does not matter, just make sure your brake fluid level is not at full level from the start from someone possibly topping off the fluid, otherwise you may spurt some fluid out of the filler cap vent while compressing the pistons.

After each wheel completed, just step on the pedal a couple times to seat the pads before starting the next wheel.

Your rear rotors disks are drum in the hat type parking brakes with the parking brake pads on the inside of the rotor disk.