I've seen a lot of DIY shows about tiling but a few things are still unclear. My next project is to tile a small area in an entry way. The sub-floor is plywood (don't know the thickness but I can find out) and it seems pretty solid. We are going to lay ceramic tile.

1. I've seen people screw cement board to the sub-floor as well as use mastic. Is there a benefit of one over the other? Would you ever use both?
2. How do you determine what thickness cement board you need?
3. Do you tape the joints in the cement board as you would drywall? Do you use mastic for the joints?

Thanks in advance for any help.