You can build multiple tents. You cannot, however, build a farm without a well (water on the map doesn't count) and the game always requires you to do that once you've researched farms, even if you don't have wells yet.
Oh? Hm, I'll give it another try and see. After I placed the first tent I never had another one come into my hand. Thanks for the warning about the farms and wells.
Edit: Oh, I see. I can add more tents from the list at the top into my discard pile to shuffle them into my hand. If there was a hint about that somewhere, I managed to miss it.