Mr Punter

For part M, better to have a ground floor WC than not. As long as your changes make it no more unsatisfactory than before, you are fine.

Bits of cut up rebar. I saw someone who bends them to shape and sells at 60p each. Search for Claymaster Fixing Pins. Really annoying if the boards float to the top, as it is very difficult to relocate them, so use plenty.

Looks cheap. What is the ballast for?

Def get a truck mounted boom pump. Have a bag of cement on the day to get the pump primed. Have an area on site to get rid of surplus concrete. The pump will discharge about half a metre of concrete and water when he is finished. Mark levels in the side of your trenches. If the ground is stable, get the trenches inspected the day before the pour.

We go for underneath an upturned black recycle box. Fine for clothes and cheaper items.

Ask the engineer to look at it again. Maybe some of the walls can be 100mm.

Have bought from IdealCombi - a large order around 280m2 but worked out about £385 per metre inc fitting (by others). Look OK, a bit like Velfac etc. Composite (ali external, wood / ali internal)

£30k

I think you are wrong. Look at Blair -v- Osborne & Tomkins for reference. Going with your thinking would mean that an architect could hold the client to ransom at any point, as building design is a staged process. I use one architect for planning (which is his speciality) and another for detailed construction information. I have, in the past, purchased plots with consent and have been asked by the architect to pay for the plans. I refused and they did nothing. Clearly the intention of planning drawings is to gain consent for a scheme and subsequently develop it.

How will you stop the cold bridge with the beam and block running through to the outside? Also, is there habitable space below?

As above - the horizontal battens only need to be 25 x 50. If you are worried about flex, install then closer together. The counterbatten / batten setup works fine even for heavy tile hanging.

Maybe use independent building control instead of local authority.

The lift and slide doors can be very good for airtightness. Also, they can be easily left open for a bit of ventilation. If you go for folding doors, do not go with a flush threshold as this seems the least airtight and most keen to snag on the ground.

400m2 is pretty epic. I take it that this is quite rural? Where I am yours would be worth about £1.7 to £2.1M and cost a minimum of £550k to build if you did a lot yourself. Quite an achievement.

I think you may need an Appointed Person to create a lifting plan, as this is not a straightforward lift. The plan should consider ground conditions, crane type, load type, load slinging, signalling / radios. Your own insurance should cover damage to the property or people, but you will need to take up the crane operators insurance as well. Crane operations are very tightly controlled by the LOLER regs and the HSE will come down hard if you ignore them and something goes wrong as a result. Another option is to arrange a contract lift, where the crane operator takes all the risk and plans the lift, but it is often very expensive.