Joining gaps between hardiboard/aquapanel

[Cenci]

Hi
I'm about to redo my ensuite
For the shower area I plan to rip off the old plasterboard and fit a moisture resistant board such as hardi or Aqua panel.

My question is how to I seal the gaps where the boards meet? Is it ok to butt them up against each other and scrim tape down?

Also should I just screw the boards to the timber studs and then tile directly onto these boards?

Thanks for the tips