Isolating motor control signals from microcontroller from high voltage/current lines

Opto-isolation is the way to go. I've used it for driving a high-voltage ultrasonic amplifier from an MCU waveform generator, and it's often used for motor drivers.

Filtering the MCU supply and the use of TVSs, such as AVX TransGuards, will avoid other problems arising from the proximity of high voltages and currents, as well as transients on the mains supply.

Optocouplers can be used in many applications but be aware that the switching speeds are limited. Digital isolators (Analog devices, et al.) using magnetic or capacitive coupling are much faster, but slightly more expensive. We have had good luck with all these approaches. Generally, optocouplers (ordinary with external drivers or drivers like Avego HCPL-3120) will do since the switching speeds are rarely over 100kHz on motors. Use gate drivers that have fast enough and powerful enough outputs to keep switching losses under control. For analog feedback consider isolation amplifiers (TI, Analog Devices) LEM's or optoamps (Avego) We will often mace the control circuitry hot and only couple in and out the control information. As far as noise goes, avoid running power through the ground of any control or measurement circuitry. Use ground planed control PCB's with a single connection of their ground to power ground if possible. I have successfully used a small 2 layer SMT (one side grounded) control board on a power system with 83 amps peak at 385 volts and 62.5 kHz and had not even a tiny bit of trouble with noise so far. The SMT is mounted directly on the power devices with short standoffs and gets its control signals through an 8 pin header.