TommoUK

If it's AIB (asbestos insulation board) its nasty stuff and notifiable work. Get someone licenced to remove it and ask them for a post completion report so you can show what has been done should you sell.

You don't have to have gas. It depends if you want it for heating/cooking. An air source heat pump and electric hob will save you the extra cost of installing gas. Will bco accept 'starlink' as an Internet solution. No cable connection required.

..this can be done. You need to consider the outside ground level, the dpc level and how far to bring your dpm up your inside walls prior to finishing to prevent damp ingress.

The Land Registry entry and plan is essentially a summary of the ownership details, covenants, charges etc. Tgis entry wont necessarily describe every boundary maintenance obligation. You need to try and get a copy (filed copy) of the original sale agreement (Deed). These are often 'filed' at the land registry and can be obtained for a fee. It's a postal request service unless your solicitor does it via their online account.

See VAT code 708. You need to work out if you qualify as a DIY housebuilder or a Developer. At face value it looks like you are a developer so you would want your contractors to zero rate their supplies.

Speak to the party wall surveyor and raise your concerns. Any damage caused to your property is the responsibility of your neighbour and the surveyors job is ensure any damage is recorded and rectified.

Put your firrings on top your joists before you lay the deck.

How do we know there is re-bar in there?

I doubt any engineer would sign that off.. regs or not. Have a look at a standard spec for a detached garage slab. You'd probably need twice that thickness around the edge.

Maybe look at cedral or hardie plank if you want a timber look. But I'm pretty you'll still need fire rating on internal face too (2 layers of the pink)..

You'll need a foundation. No point risking all the effort and cost to find out the slab breaks under the weight.

Good option but on a terrace you would probably then need a daylight survey as it breaches 45 degree rule

Yes, many times. You can of course put the stairs the other way but you end up no better off for more cost. And if you go up in to the loft you want to try and 'land' in the highest part.

..try and have a masterplan even if you don't build it all at the same time. Yes take out the chimney to make more room in your bathroom and future loft room but you will need party wall agreement.

Have tried. Forgive the scribbles as Im on a train. I would position door to rooms to provide light to the hall/landing. Your next flight of stairs to a future upper floor would mirror existing stairs.