You can get a Carriage tour, AND a Harbor boat tour for a combined price that is lower than the two are separate. We did that last trip. On both tours you will see most of the sights, and get a LOT of Charleston history. Well worth the price, and time.
However. to really see Charleston. You have to walk it at your own pace. To see, and enjoy the town. You will need more than one day. To see the other sights, Like Patriots Point, and the Plantations. You will need a couple more days. You cannot see much in just one day.
FYI. On a Ghost tour. We learned difference between a Cemetery, and a Graveyard. We also learned that to be buried in Charleston proper / on the Peninsula. You have to be born on the Peninsula.
LOTs of stuff to do.