Mr Punter

Neither is landscaping but if it is on the approved plans it is recoverable.

+1 Ensure stud, washers and nuts are corrosion resistant (stainless or galv). Clean the drilled holes thoroughly.

The Party Wall notice engages the Party Wall Act and once issued, you need to follow through, possibly instructing a surveyor and perhaps also paying for the adjoining owners surveyors surveyor. You will need plans and sections, together with Risk Assessments and Method Statements from the piling contractor. Allow 2-3 months. If your neighbour does not give their written consent to the proposal, they will be deemed to be in dispute and 2 surveyors will normally be needed to draw up a Party Wall Award - all paid for by you. If you chose not to issue the notice and just carry on, you run the risk that the neighbour could issue an injunction preventing you from continuing, but they would need to do this at their own risk and expense. If their injunction is successful, you would be liable for their legal costs as well as any damages. If they do not issue an injunction there is nothing else that can be done.

Where we are you have to have an accessible ground floor WC with outward opening door that can be made into a shower room. Probably 1.6m x 1.8m. Better not to have the kitchen open to the stairs, so add a door.

We had an Ebac and it really heated the room up which was not good. The Meaco is much better. Less than 200W. I have a couple in a basement rental, with permanent drainage, and they keep the damp at bay.

It is best to seal all the cuts with their touch up paint but I think it is more for aesthetics than durability. With a butt join it would be best to have factory finished ends and join on a support.

We have a Meaco dehumidifier for clothes drying. Very cheap to run and dries brilliantly.

I have done similar but with 600 x 600 tiles 18mm and a pedestal in each corner. Make sure they are non-slip. There is not much room under so you will need to set the pedestal heights and positions spot on as you won't be able to adjust them later. Laser level may be useful. The fillet under the sliding doors looks a bit awkward.

I have used plastic lumber for below ground. Over twice the price of timber and may not have good fire rating for cladding but it does not rot.

Yes, 50mm concrete screws are your friends here. For a 7.5mm screw drill a 7mm hole and clear it out a bit so the screw goes in tight with an impact driver but does not lock up before it is home.

One nail per strap looks a bit stingy. Often see screws and plugs or masonry screws. No issue with zipping off the surplus strap with a grinder and thin blade.

OK in theory but this never ever happens on site, which is why the "plasterboard tents" are notoriously freezing.

In reality this is more likely to lose heat v solid plaster, as it can allow cold outside air to circulate behind the plasterboard. This can be very significant and difficult to resolve. Another failing of SAP.

Unless this is a strict planning condition you may find render is more acceptable to future purchasers and lenders. Probably cheaper and quicker as well.

I don't think you have misread. It looks like a thin coat render onto mesh on carrier board, so probably 6mm thick. God knows what has gone on and what to do. I would go back to the architect and ask for their suggestions.