How do I bathroom / kitchen / extension? etc.

Yeah cutting into bedroom 3 as others have said could do it stair wise.

The way I am doing a loft...

1. Look up every loft plan on the planning portal for E17
   
2. Do 10000000 plans myself based on previous architects drawings
   
3. Research cladding for 4 months.
   
4. Create extensive Figma and Notion files.
   
5. Find cheapest builder
   
6. Spend 6 months trying to get blood from a stone (aka an email reply)
   
7. Bin off said builder who is a prick to the cost of £2K
   
8. Find a more expensive builder thats a grown up that I should have chosen in the first place
   
9. Another 6 months deciding on window size and shape.
   
10. Get party wall going as neighbours always object to any work getting done because they can.
    
11. Get plans redrawn by grown up (actual architect, not draftsman as per loft companies us).
    
12. Melt.
    
    

I'd prob do it slightly differently to the above to be honest, just make sure you don't end up with PVC windows and you'll be fine.

Also everything @Sheppz said.