ᐅ Insulating an Old Farmhouse: Preparing an Uneven Facade – ETICS or Ventilated Façade?

I live in an old, mixed farmhouse: the ground floor is masonry, with aerated concrete in the extension, and the upper floor consists of timber and clay plastered with a roughcast finish. The aim is to unify and insulate the exterior. One side still has exposed timber framing, while another shows two different paint colors from repairs, etc. Removing 300 square meters of old cement plaster from the former East Germany period is really not an option despite the motivation. Simply insulating over it is also not ideal. I’ve heard many opinions – some say that with a ventilated facade the soft insulation material will integrate well and that’s fine. Others recommend an ETICS (external thermal insulation composite system) using adhesive methods designed for uneven substrates, arguing that this will prevent the creation of a ventilated cavity.

There is also significant unevenness due to a beam – about 5 centimeters (2 inches) difference. Some suggest compensating for this by using insulation of different thicknesses, for example 16 cm (6 inches) and 10 cm (4 inches).

So –
How should I prepare the substrate – patch, repair, clean, smooth? As much as necessary, but as little as possible. I am fairly certain that this rough, porous plaster harbors pests over winter; woodpeckers are regularly active there too.

Or am I overthinking this and will a professional insulation installation simply seal it properly and solve the issue? Which insulation system do you consider the most sensible: ventilated facade (VHF) or ETICS?

Attached are photos of the most extreme spots (damage from hedges/climbing plants and the pronounced difference caused by the beam).
Thank you very much, I look forward to hearing how you would proceed.