Then why the hell are there four hundred slots on the grid? >_>

Some missions only appear in certain cities. Also, have you checked your Quest Report? It lists unavailible quests, and you can follow the quest chain lines to find what should be next.
Yes. The only quest that A) I can do, and B) has a line coming out of it to show that there's more to the line of quests is the Nu Mou and the Rupees, and I tired it again and nothing happened.