Any special kind of tape? is the support of the studs enough for CBUs without any additional bracing to screw them to? What about ceiling, does it need any slope, I may need/want to tile the ceiling over the tub, if so there will be a box dropped from ceiling to support track for floating shower closure panels. Thanks

The tape is called sheathing tape and is red or white in color. It's used for Tyvek seams, Styrofoam board seams and poly vapor barrier seams.

The ceiling does not need to be sloped. That's only a requirement for steam showers.

Ceiling joists should ideally be on 12" centers for cement board but not absolutely necessarily. Make sure to follow the manufacturer's installation instructions for the product your going to use.