First ?. Not that important. You will lose some of the rated power but you will not hurt the amp, in fact, it will be quite happy.
Second ?. Sometimes ok, sometimes not. The lower the speakers impedance the harder it is for the amp to deliver the current from its 8 ohm tap. Usually it's ok to try different taps and go with what sounds best.
Second ?. Sometimes ok, sometimes not. The lower the speakers impedance the harder it is for the amp to deliver the current from its 8 ohm tap. Usually it's ok to try different taps and go with what sounds best.