1 and 3 are easy to answer. Because tariffs, like EOs, are something he can do with a stroke of a pen (ignoring for a second the improper delegation by Congress of the constitutional power to regulate trade).
If you give Trump a power, he will use it. Trump has the tariff hammer and he is out looking for nails. He wants to swing that hammer because he likes to exercise power for the mere sake of exercising power. Trump enacts tariffs for the same reason people like to climb mountains -- because they are there.
Also, Trump has had a long-standing belief since the 1980s (when Japan was buying up Manhattan real estate) that the US is getting the short-end of the stick in the new international world order. No matter how much logic or economic analysis is presented to him, his default belief is that other countries are taking advantage of us. So, swinging the tariff hammer makes him feel like he is doing something to combat unfairness.
These two points -- his inclination to exercise power that does not require congressional approval and his distrust of the current world order -- explains why he enacted the tariffs.