Blech and microwave

Question

1. I saw your answer regarding heating something on the blech. You wrote that you can heat something if it is put on a pot which is on top of the blech. But doesn't your father say (in the on-line shiur) that it's good enoiugh to cover the blech with tinfoil, and you don't actually need a pot? 2. I looked over your answers regarding Pesah and the microwave and it is not clear to me. So let me ask, now that all eyes are on Pesah. Does the microwave need to be kashered in any way, or is it sufficient to simply clean it well? 3. In general, do the sides of the microwave absorb taste, so that if something falls on them and cooks it would be a problem (I think most are made of some sort of metal).