I'm quoting Thaddeus in the question you linked :
>Under a red sun, he appeared to be Human in all the ways that mattered.

Thus, the answers :

 1. He could be affected by any drugs.
 2. He could be addicted to any drugs.
 3. You say it is "quite hard for a common person to conquer the addiction by his/her own will". Superman is no common person. So I guess he could, even if it would be hard.

Not really much more to say, since the details are in the question you linked.
Maybe one more thing : if Superman was addicted to a drug under a red sun, I suppose as soon as he would get under a yellow one, the addiction and effects of the drug would fade instantly.