JohnMo

This mine 2x 5 port (hot and cold), single feed, no flow issues.

Why so complex? Just buy a bog standard manifold such as - first one I came across https://underfloorparts.co.uk/product/plumbing-manifold-5-port-with-service-isolation-valves-universal-hot-and-cold-water/?srsltid=AfmBOorfGw6dC3Kp3bBGSXzk3717nPjKeRyytjno3wxLyrTh9oFQOkhaIOA&gQT=1

I just got my ground contractor to do it. Normal concrete lorry and in our case, but because of distance and access, we use a concrete pumping lorry also.

I wanted as the OP to do the screed before walls, so just used a normal concrete, it really doesn't care about the weather. For clarity we have zero screed, just concrete over the UFH pipes. My build-up is 200mm rebar concrete slab, then 200mm PIR, then as described further up thread.

Buffer and secondary pump and zone valve just delete them - are they needed? Most likely not.

No switching of switches required, it just does it automatically both ways. Generally no idea if there is a power cut anymore. You can see a change in trend data on the app if you look.

Depends on the inverter. I have an all in one AC battery setup, it keeps G98 approved PV inverter online with mains off. It also delivers a continuous 6kW plus PV output with mains off.

Yep No, like this, insulation (PIR) polythene barrier sheet, UFH pipes clipped to insulation through polythene, then 75mm of concrete. Power float smooth. Just like this

Just do concrete, not screed. No effect once cured with weather. Just do fibre reinforced if you need anything. We concrete with fibre 100mm thick.

Doing it again, I would most likely do a version of twin stud construction. And construction stick build on site. No big deposits to companies, builders merchants only delivery as required.

Pretty much.

Only once had an issue, but tried to light it in 60mph winds it wasn't happy. Now just use a fire lighter and it starts every time even with 60mph winds

You need to clean more often. Just get the window cleaner to do them, ours uses a demineralised water and a huge extension brush arrangement, so is done from the ground. Most window cleaners do it that way now. We clean our twice a year. You don't need any chemicals or other stuff.

Why not ICF, pretty easy DIY option. Our walls (200m² single storey upto 3.5m tall) took two of us 4 weeks start to finish.

We had our fire (stove on) when temperature dropped very low (about -6 and below). Although the room temperature was still about 20 to 21, it just felt cooler. Lit the stove and moved the house temperature up a little. Secret is don't overload with logs, heat output is proportional to how much fuel you add. Other factor is get soap stone covered stove, this slows down the output curve considerably. And use the air regulator. Decommissioning - empty ash bucket, done. 5 minutes later complete. Low energy how and stove works, just a matter of sizing correctly, specify correctly and use sensibly. Our first use of the fire caused overheating, but I fully loaded with logs, so no wonder really.