My story might serve for contrast and comparison...
To rotate our roof TV antenna I purchased Radio Shack's motorized antenna rotator. ($70 thirty years ago.) The roof unit had a large motor which turned the antenna through 350 degrees. The armchair unit had a small motor turning a dial labelled with the four points of a compass.
The motors were geared to turn both indicator and antenna at the same speed. To get the two aligned, I had to spend some time trying different positions of the dial, then stepping outside to eyeball the antenna's direction, north-south-east-west.
I don't know if this method is less expensive or less effort to construct than your planned project.