Using slip rings IS the way to go and you have several options:
- Buy real industrial slip rings (expensive).
- Use a 1/4" jack plug with home made brushes (might wear down faster than anything else, as they're usually made from soft copper with a nickel plating and once the hard plating is worn out, the copper will soon follow.
- Make your own from the ground up from pieces of copper or brass tubing mounted on a (rigid) plastic tube and run the wires inside the tube - then make the brushes from bronze.
Power lines should have a capacitor connected to smooth out brown outs and signal lines would be helped with small caps calculated for the frequency and waveform, but a carefully worked out protocol could handle most of the possible noise - use a light dab of grease between slip rings and brushes to keep it from oxidizing.
For the signals, you could modulate them onto a carrier wave and have them capacitively connected to the rotating turret as well. with such a frictionless setup, it doesn't matter how far from the center of rotation the cap. coupled rings run, but with brushes there's friction, so keeping it close to the center will minimize the drag.