can i plug my micro cube into an external 4x12 cab? how many ohm's is the MC? would it power the 4x12?
It doesn't have an external speaker jack, so unless you open it up and re-wire it to have one you won't be able to plug into an external cab. You could do it with the headphone out but it would be very quiet.

It doesn't matter how big a cab is or how small an amp is, any amp can drive any cab. There's no mimimum amount of power (within reason, of course) required to drive a cab.