This work is not simple. If it was you wouldn’t be asking.
This work is notifiable to your Local Authority. They’ll charge you a couple of hundred quid to inspect your work as you muddle through the process.
But if you won’t pay a professional you probably won’t tell your Local Authority either.
So, with that in mind, it’s simple.
To avoid detection get hold of material that can’t be dated, eg cabling ripped out of an old installation that pre-dates the current wiring regs.
Red and black insulation. That’s the key here. If anyone asks says it was like that when you moved in.
Use that empty shower mcb to attach some of this old twin and earth (remember to lick your fingers first) then string it out of the nearest window, peg it to a washing line for extra support and feed it through a hole in your cave wall. Terminate it inside an old metal dustbin where you can daisy chain a load of terminal blocks, each one feeding the different circuits.
If you’re not sure what size terminal block to use look at the wattage of the appliances the circuit will feed, ignore the number, put your finger in the air, close your eyes and pull one out of a lucky bag.
Once all the circuits are connected, remember to put the lid back on the bin to stay safe. You could tape it on just to be sure.
Remember also to check the maximum Zs value using any method you can think of.
That it I think but please have some unique dentistry work completed first, so it’s easier for your charred remains to be identified.