Batten aquapanel onto pastered wall?

Hi guys - my first post here.

I'm tiling my entire bathroom - floor to ceiling with 12mm travertine (60x30cm)
The walls are a mix of solid granite with lath & plaster (mixture of sound and unsound), stud plaster board and plastered breeze block.

My intention is to batten onto the existing surfaces (plastered stone & block walls) using 32x32mm battens and fit aquapanel ready for tiling. (Stripping the plaster back to the bare stone would be a nightmare and 80% of the wall is a sound finish)
For the PB walls I'll replace the PB with aquapanel as I read on here that aquapanel can take the weight of these tiles.

Is this a reasonable approach?
Is there a cheaper or easier way of doing this? (I have assumed I can't tile directly onto the plastered walls in shower/bath area hence batten/aquapanel)
Have I missed anything obvious?

Thanks in advance!

 

e.g I assume priming the plastered block wall with SBS and tiling directly onto that without aquapanel is a bad idea?