1) the strange chest is there just to tell you "drugs are bad" or sth like it. After the mushroom farmer caught you completely stoned, he wisely locked his chest. The only advantage of opening it in the first place is that you now have the mushroom farmer to trade with (not a big advantage if you ask me)
2) Lever: after you get the quest, try the lever, talk to the good merchant (you can convince him to go outside); now you can pull the lever
