I’d suggest revisiting the design and going for infill constructional slabs, raising the concrete up, dropping the insulation down, and having the UFH pipes in the slab (have a look at insulated raft foundations on google for context 😉. No need for screed then.

We’d need some details of the thresholds to add other comments!

Your internal floor level is 375mm above external ground level. That won't work for a level threshold. At thresholds you can run the insulation and screed to the outer leaf, with perimeter insulation of the screed and DPM detailing required. The won't be an inner leaf of timber frame.