Who has done your inspections to date? If you have a name it would help. Give him a call. Bear in mind it is the end of Easter hols today, so next week should be better. Unless they are no longer doing Building Control (which they are legally bound to carry out) you should be able to get someone out fairly soon. Be nice and don't lose your rag.
There will be loads of solar install firms who work near you. Get 3 quotes and pick one. It may be that they will not fit used kit or have wiring by others but you can ask.
I think similar or more expensive, depending on the range. Roseview are based on standard upvc profiles from Rehau and do lots of extra customisation and finishing. Their top range is almost indistinguishable from timber.
If you are not in an exposed location you could have got away without these as the render would stop water getting through. You probably have weep vents every 450mm but some have been covered by render.
You could have a dig about to find more or cover up any you don't like, but either way it is very difficult to make it match in with the render.
No I didn't mention EWI. You need to fit counterbattens on top of the rafters and fix through the externally fitted insulation boards, hence long helical fixings needed. No need to fill between the rafters, although you could use a small amount subject to satisfactory condensation risk analysis.
If you have external insulation you will need to work out how to fix battens / counterbattens. You will need a lot of very long fixings. I think the helical type work well. Expect to spend about £7/m2 in fixings for counterbattens.
No, not viable. They are perforated clay and have poor insulation values. Warranty providers like a drained and vented cavity, so a single skin will not work. The blocks shatter if you drill them. You will struggle with plumbing and electrics. Airtightness is hard to achieve. More expensive than normal blocks. Just move on from these and save yourself a headache.
When the cavity is fairly wide the risk of voids is almost eliminated with blown eps beads. Probably the safest choice. Also if they miss, say an entire elevation it can be filled later.
Sometimes I have had the sockets on a flex under the units. Quite a few appliances have moulded plugs and it may be that any warranty can be voided if you cut them off. It is not simple to anticipate what is needed. I have had induction hobs needing hard wiring on a separate circuit where others are plug in 13A.
I like under cupboard lights to be switched from an extra gang on the main light switch, which can also be a challenge.