Vaporetti (public transport) are larger metal boats, while water taxis look like cool smaller wooden boats with cabins. I believe some may even be labeled TAXI. When you arrive and see them, you will immediately know the difference, just as you'll know a gondola when you see one.

The casino is on the Grand Canal, can't give you an estimate of distance, but know that you could walk from one end of Venice to the other in 45 minutes. It's closer than that (20 minutes from San Marco?). The summer casino on the Lido is a longer boat ride away from the main island.