It's a tricky one, the NA is all moisture tolerant and a very good screed when applied correctly. Likewise Laminate floated on a underlay with DPM and tape does have an element of moisture tolerance to it as well.
'by the book' would be to take up what you can, re-dpm, NA properly all at quite...
This sounds like a project a little too far as the floor needs moisture testing and then the screed levels need looking at closely to understand how deep the levelling needs to be and what primers to use and how to manipulate and build up as and if required.
The LVT will only be as good as the...
Universal Ally Ramps will do the job but will look like what they are, cheap!
Have a look at CAT profiles or possibly Gripperods Premium range, they may be a bit cheaper than Stairrods UK
Once you encapsulate the UFH as described above, do you have the TOG rating of the UFH system?
Ideally you shouldn’t overload the UFH system and it should have a TOG rating that the underlay and Laminate flooring should not exceed combined.
The best UFH underlay for Laminate and wood floors...