We have the 4 x 3 version of the one you’re getting, really impressed with it.
I cheated with power and simply use an extension plugged in via an RCD. In the ‘shed’ I’ve attached a couple of doubled sockets to the wall with simple plug in lights. I’ve no real power load in the shed and no computer so manage to stream youtube to a TV for the turbo trainer, via a pair of plug in wifi extenders. I used sikkens wood preserver on the outside, 4 coats to date.
I insulated floor and ceiling but not the walls…we have the 44mm wall version, way more solid a construction than the 28mm it replaced. (Painted the walls) But we don’t spend hours in their thru winter so perhaps see how you go on thru the coming months before committing to more work/expense?
I bought a roll of roofing membrane and attached that to the roof first, then the roof felt. Happy enough with it so far.
Good luck with it