I'm going to recommend against electronic feedback unless you are a
control systems hobbyist... I did PID
(proportional-integral-derivative) servo on a homebrew rotating mast so
I didn't need a readout and eventually decided to go with a rotation
sensing pot, a voltage-to-current converter, and a surplus meter.

This was after I tweaked the PID to get rid of the oscillations but
still had some average position errors...

I guess with a digital system it would be easier to optimize. Mine was
all analog... and only one op amp, so the settings interacted :-)

Making the motor go and watching the meter is a more sensitive and
intelligent form of feedback, as long as you've got a system you can't
break by turning too far.

A simple pulse-width-modulator for speed control might be in the cards
though. That way you send a variable duty cycle full-on full-off pulse
train to the motor. Good torque and you don't need a variable power
supply just to run the rotor.

I'm going to add one to my rotator soon... I've got that on manual
right now... pulsing the switch makes a nice slow smooth rotation!

If you do like electronics projects for the sake of electronics
projects, feedback control is an interesting way to go, though.

73,
Dan
N3OX