Conor

I made sure the washout area was a spot that would be later paved / concreted over. Each time there was a dump of concrete or cement, I'd rake it out flat and level. Ended up covering a good 20m²+ and 100mm+ thick by the time we were done. Concrete pumps produce a lot of waste!

Don't do any filling now, give it a year to let any drying/ movement/expansion/contraction finish off. And when you do, rake out any narrow cracks with edge of a paint scraper before filling.

Maybe. Pro: longer PRV life Con: likely to get clogged and reduce flow over time. Regular cleaning needed. In water networks, strainers cause more issues and cost than they save. Primarily because once they are fitted, they are forgotten about. Hidden. Don't provide a day to day function, and no telemetry giving any idea of condition or functional performance. If you do fit one, set a reminder on your calender to clean it every 6 months.

1.8m from local ground level. no limits on hedges.... Get some 6ft Griselda/laurel/box for fast growing screening. Wouldn't plant this time of year tho, we're struggling to keep our new beech hedge alive in this weather

Key thing is the steel to concrete ratio along with spacing between the mesh. See if you can use this to do a quick check. https://wutools.com/calc/engineering/rebar-calculator

Welcome. First thing will be to get a drawing from Severn Trent showing the location and details of the sewer. If there are any discrepancies, request they come out and survey it to confirm. Check your property deeds for a way leave. There may not be one depending on the age of the sewer Whether you get permission to build over or not, that's a complete lottery I'm afraid. same for planning. Precedence a couple miles away doesn't really apply, it's what's been done on your street. Best of luck. Ask as many questions here as you like.

No need to fix down once you get worktops on and fill the cupboards.

Is it just a vent pipe or is it a function stack? If it's just for venting, bury over it, fit another one somewhere else, or use a combo of air admittance cables instead.

200mm is a bit out of what you could call a margin of error. we did similar, ended up 250mm too high by the time we got up to the ridge. I made the call to drop the wall plate by 100mm and the ridge by 150mm. So we edend up about 100mm too tall. Could not got away with any more as we set the ridge height to be mid way between the houses either side of us. It depends on your design and construction method, but trimming 100mm off your ridge and wall plate might help you sleep at night. we were building ICF and a panel roof system, sownqs dead easy to make the change.

Internal on painted steels. Not a clue where I got it from, was five years ago.

I used foil faced aerogel, easier to work with and stick down. I think I used double sided tape.

We (un)subtlety told the surveyor the valuation we needed. He did this on all bar one occasion.

My architect always said anything within the dimensions of a concrete block would probably be ok with planning.

It's easy. You can certify it yourself with an anerometer and a spreadsheet. I think there is an MVHR design sheet floating around the forum somewhere. Tl;Dr, make sure your duct runs are as short as possible and your diameters are as big as possible.

Depends on the valuation. The getting out of the ground stage is the most expensive part, but also adds the least value. You really want some walls built before you get the valuer out. Get as much money as you can at each stage. Our biggest regret is not drawing down more!!!