Re. measuring the current. The problem with linear opto-isolators is that they are not linear. Donatas does not state what precision he needs, but if high precision is needed, the linear opto is out. Using a current transformer is one option, a good one will be quite faithful down to 10% full load. If precison is required over the entire range, the solution is to build a floating unit with a series resistor (typ .1 ohm or less) an adc and a couple of DIGITAL optocouplers.

Have fun and be careful

Erik