Between the base and the base plate there is space for a 608 bearing to make the rotation smoother although I did the test print with a 3D printed bearing and it works good enough for me.

I also designed some dividers ( one long one and two small that looks in between). each divider have holes on the top so you can customize how high you wanna go (each divider is 20mm high).

Finally I did two top plates, one with holes so you can keep adding levels and another one without the holes to use as a final top.

I printed with standard settings (15% infill, 0.2 mm layer high) and some small support.