Mr Punter

Yes you can tile these. I am not sure why they would need to "breathe".

Normally you will leave the battens short of the window opening so the air can flow round. Like this:

Tee off the below ground. Come up to near finish level and use a 110 to 40mm reducer for your sink waste.

Have you looked at loft legs? They could raise the height to give you more space for ducting, cables and insulation. It will reduce height though. I am not sure why you are proposing membrane.

A plate like the one holding the hinge, so it has more than one fixing and they are spread out.

If this is just surface water you can pretty much do as you please.

This is why it is important to identify the wires with the correct colour sleeving.

The south facing units are the ones that die quickest.

@Gus Potter of this forum is a structural engineer. You could pm him and see what he suggests. I have not used him but he is based in Scotland.

It depends on the inspector. Since this is for your own occupation it won't come back to bite them so they could be OK. You may need to properly cap off the waste pipes sufficient to do a soil pressure test. Do you need warranty approval / mortgage drawdown? They may be a bit more picky for this. You need electric completion cert and you will also need an airtightness test so see what state they will accept.

No, but I remember a fair amount of effort on my part. Probably a Euroscrubby and some Bar Keepers Friend.

I put him on ignore a few years ago as I thought he was trolling.

Use the fattest stud that will fit through the holes. Use the plate as a template. 100mm depth in the concrete should be fine and 2mm bigger diameter than the studs. Either a blow out tool or a hose to clean the holes.

Measure the holes in the rollers. Your stud should be snug but not tight. It is probably M12.

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