Mr Punter

OK so just backerboard the sides and tile the lot. No piss coloured grout though!

Rendered and painted? Maybe some render board for the reveals.

It would be a good plan to remove the plasterboard from the inside so you can see what you have there. I imagine there are several load bearing studs between the small openings plus either end. You will also need to see how the top has been designed. Once you have opened this up you can get an engineer to do the design and calcs. Bear in mind the timber frame may be taking the roof and first floor loadings.

Timber frame has been around for ages. The insulation and airtightness standards 30 years ago were nothing like as stringent as they are now. If it has a brick or rendered block outer leaf it should be easy to insure and mortgage. No specialist trades needed.

Yes, get insurance. The main purpose is for claims made against you for personal injury, death and damage to your own and 3rd party property. It should also cover you if the subbies insurance is not adequate.

Is it still to be used as a barn?

Just look at the cost of removing the wall. You can re-use the kitchen if you want to. Also, why are you plastering if you are considering rebuild?

You will need to submit new plans with the correct orientation. Let the planner know and they may agree to extension of time for their decision.

Another vote to remove the wall.

Cut the tarmac nice and neatly and sand / cement bed a soldier course or 2 of the paving blocks on the concrete.

There are other standards that are acceptable. Mostly this relates to doorsets rather than just doors.

The insulation value for the wood wool panels is pretty poor. Unless this is a cowshed or you have further insulation above, you may want to reconsider.

So will you park widthways across the house? It looks doable. As you are not creating a new access from the highway you may not require consent. It may be better to reverse in.

The openings would be quick, clean and easy to make if you hire a petrol cut-off saw with diamond blade and attach a hose to it. Just make sure you have a steady platform for the higher bits.

You could try https://www.paramountse.co.uk/ They did a full set of calcs for a project for us.

I would leave them in to ventilate the cavity and keep the wall dry.

It could be jointing compound, but I have only used it on a flat surface.

Did they have the drawings and spec for the install? Were the installers supplying the tapes and EDPM trays?

Perhaps not even an effect: https://www.mcgill.ca/oss/article/critical-thinking/dunning-kruger-effect-probably-not-real

I guess you could get some H10 bars bent to the shape and allow for a 500mm lap to the mesh, then tie further H10s at right angles at 200 ctrs. It looks like you will only need about 6.

You may need to use a soakaway for your surface water, especially if you propose more impermeable area v. the current arrangement.

The drawings only show a cantilevered balcony about 1.0m deep, not the 1.5m portico arrangement you have built. I can't see any issue with the piers moving once you land the planks on them, but can you run it past your SE?

My pet hate is when they are twisted so they don't lie flat.

Get your solicitor to request a Building Regulations Completion Certificate from the seller.

I would say no to the membrane and no to the sprinklers. The membrane will not do anything to keep the weeds down and is very bad for allowing the soil to aerate. The sprinkler will waste loads of water.