Playing a land from the top of your library counts as your land play for the turn. Once you play a land during your turn, you won't be able to play an additional land from the top of your library unless another effect (such as that of Azusa, Lost but Seeking) allows you to.

Courser of Kruphix doesn't change when you can play lands. You can do so only during your main phase when you have priority and the stack is empty.

While playing with the top card of your library revealed, if you draw multiple cards, reveal each one before you draw it. If you put multiple cards on top of your library at once, reveal only the one new top card.

If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you don't reveal the new top card until you finish doing so. This means that if you play a land from the top of your library, you can't look at the next one until you've handled any replacement effects that modify that land entering the battlefield, such as that of Vesuva.