Mr Punter

I think it would be worth getting a topo survey done so you can see what you have got. You can then work out what you would like (bin store, clothes drying, bbq , seating etc) and plan the space and areas and how they will connect. Is this a DIY project?

It looks fairly simple. You should not need an architect. You are right that the kitchen will need a door to the hallway. You engineer will need to take a look and see which way joists run, floor type etc. Who is doing the work? You could do this on a building notice rather than full plans.

They will sometimes just want pictures but if you request a quick visit they should agree to it. I assume they inspected the foundation trenches?

I would arrange to meet with Building Control on site. Let them break the news to the "builder".

They often like to see a drained / ventilated cavity.

If the beam is supported along its length you will be fine, if it only supported at the ends you are not at all fine.

If you clad a house in unpainted treated softwood it will last about 10-15 years. Clad it in untreated imported Western Red Cedar and it will be good for 50+.

I have done a feature brickwork fireplace directly off beam and block. The floor designer specified multiple beams for that section - something like 10 together. We could have done extra footings for similar cost.

You may find studwork is easier.

You will be OK with thermalites. You can't rest the roof joists on them though.

I doubt it is holding anything up. Take out the coving and some of the plasterboard at the top and have a look. Beware of asbestos in this age of house.

I think it will need packing out. You could use the Marmox type boards which are lightweight and easy to cut.

I doubt the mix will make much difference. I have seen tests on some of the batch mortar and it can sometimes be a third of the advertised strength. The DPC is annoying but survivable. I assume the inner leaf has a proper DPC and if so you should not notice. If you do have issues you may be able to rake out the 25mm and repoint using waterproof mortar.

That TLX stuff is pretty flammable. Try holding a lighted match under it for a few seconds. Be very careful with plumbers torches etc.

Most commonly you would just trim out the floor joists and infill, plus provide electric to the location. Installing and maintaining a lift is expensive. If you are wheelchair bound it would be very dangerous to be upstairs alone when the lift fails.

Perhaps you could submit the previously approved 2 house scheme so you buy some time and have a valid consent. Later you could even start the construction so the consent is locked in.

There is quite a gap where the door opening is. Maybe it should have handrail and toe boards either side!

3 trestles and 4 planks.

You could just build a lightweight timber frame to support render carrier boards, like Bluclad. You could screw into the underside of the arch for support. You can then mesh / render the whole thing.

OK here is photo example of some "work" that was carried out on a tenanted property we own. Not surprisingly I refused to pay. They were supposed to renew the lead flashing. He persisted in trying to get payment and threatened to come back to the property. We politely said he would not get any money from us and it would be harassment and criminal damage if he attempted to visit the property. This guy has 100% positive google reviews and his modus is to get the customer to write the review while he watches them. There are some right cowboys around. This was a £450 job:

Criminal damage carried out by morons. Not big or clever.

When we have done car chargers the sparky did them in armoured cable.

I think running the cable internally would be better. I don't think you are not supposed to run cables in the wall cavity, which is what your batten space is.

I have a bad feeling about this one...

You are best approaching piling firms. So much depends on access, location, temporary v permanent. Mobilisation could be £2k.