sorry about the poor piccy, but we've got this. Lintel steel just resting on the cripple studs, racking steel (on a steelpost in the inside wall of the room) resting on, with the upstairs walls again just resting on. All from the drawings.
IIRC the premium uses the slightly more flexy duct.
I paid for my design, as I wanted it prior to buying the stuff (and ended up getting the unit elsewhere), I think it was £100 or £150, and it was credited against the subsequent order as I recall
I got a few sheets of 10mm XPS to do the reveals, but I've only done the bathroom windows and think I'll do the kitchen ones but don't really see the need to do the rest.
Local B&Q recently clear some 2-temperature bulbs for a few quid. Switch on as warm white 35W tungsten equivalent, toggle the light switch and they're 60W equiv cool white.
I went for the Iboost+ and it's not bad. Our meterbox is 15m away, behind 40mm of foiled PIR and a reflective VCL and there's no issue with signal. I picked it up used so it isn't on the latest software; this means it starts diverting at 200W or so. The latest ones are configurable between 100 and 500W I believe, to allow better integration with battery systems.