1. Could a horizontal axis of rotation be used satisfactorily in an experiment uniform circular motion? Explain

Answer 1

Only if the center of mass of the rotating object lies on the axis (as with a rotating disc, for example). Otherwise, gravity will introduce a time-dependent torque that will make the motion nonuniform (slower at the top and faster at the bottom).

Answer 2

yes, it can, one does have to consider gravity. I will gladly critique your thinking on this.