heavy weight

I have seen considerably more weight used on this table. The more mass that is rotating the more even the rotation. With idler drive the problem would be the transmission of vibration via the drive wheel and more mass will damp this to some degree. I don't think it will be a problem.

I don't know what might constitute excessive weight for that table, but, it is generally the case that too much weight will cause excessive wear of the thrustplate and the ball at the end of the spindle that rests against the thrustplate.

Too much weight also could cause excess transmission of bearing noise to the platter. There are some turntable designs which go to extraordinary measures to reduce the weight on the bearing to reduce noise transmission. Such measures include magnetic levitation, cushion of air from a pump, etc.