Remove very coarse trowel render for ETICS

We have a house from the 70s. The masonry is made of pumice stone. The exterior plaster is firmly attached to the wall. It is a VERY coarse trowel plaster, which was applied very irregularly and with many high spots (partly several centimeters).

We need a relatively smooth surface for our [WDV-System]. Now to my question, how do we smooth out or completely remove this terrible plaster? What options are there for such plaster?

Attached are a few pictures, thank you for your suggestions.

We need a relatively smooth substrate for our ETICS.

Which system and what are the specifications of the system provider? What does the processing company say?

Now to my question, how do we get this terrible plaster smoothed or completely removed? What options are there for such plaster?

- Sand/blast cleaning (but this damages the pumice when the plaster is removed) - mechanical removal ("hammer and chisel" or appropriate tools) - smooth plastering Do you want to do this yourselves or should a professional company handle the preparations?