If at any point you could be considered to be giving professional advice you should have Professional Indemnity, this includes literally every time you design a circuit.
Its hardly new people have been making this up with Click Minigrid for years, we usually just run the whole bathroom off the 3A to eliminate the risk of the S/L remaining live easy enough to do, 3C+E to the switch 1 core for the permanent live 1 core to send the switched live back to the fan iso...
Split the tails before the RCD, install one S type for the main supply and one for the outbuilding. Id probably go 3 core SWA and drop a extra rod as long as the separation distances are fine
Theres nothing complicated inside them(This is the GARO EVSE Tester) it basically allows you to test the actual operation and safety features of the charger.
Single insulated must be in containment and may require de-rating. Specific regs? come on youre supposed to be an electrician why dont you start in chapter 4
Probably want to be looking more to 60204/60079 for guidance in this situation rather than BS7671, there are plenty of 24V connectors that are Ex rated not cheap tho(nothing Ex is)