A splendid job!
All in favour of insulation. Stops or minimises condensation and keeps the place cosy.
My shop is about the same size and a 2 Kw fan heater soon brings it up to a comfortable temperature.
It was painted gloss white when first built, walls and ceiling, to make it as bright as possible.
It may be a good idea to put in a couple of small floor level m,vents so that moist air can exit, rather than accumulate.
I also have a 6" intake fan, mounted high up, when additional ventilation is required . The exterior vent has a long, downward pointing, hood to prevent ingress of rain.
Internally, it now has great similarity to Rubik's Cube.
Power is supplied from a RCD in the house, to a ring main above the bench, feeding no less than eleven double metal clad sockets. The one supplying the VFD for the lathe is a suppressed one, to prevent any nasty "spikes" being fed back up the mains to the detriment of our house and any other on the same phase.
One day I should fit a proper Garage unit to supply the lights and sockets; but tomorrow never comes!
Lighting in addition to the work lights on the machines, and above what little of the Fitting bench and Vice can be seen above all the rubbish, is by two individually switched 4 foot 60 / 85 watt fluorescent tubes.
Should really replace with LED tubes!
Security is important. You do not want the damage caused by breaking and entering, or the loss of items which have cost a lot of money and / or time.
Make sure that the doors are sturdy and not easily distorted.
If need be, have two hasps, or bolts, at the upper and lower quarter height points of the doors, that can be fitted with good quality padlocks.
Use coach bolts, with domed heads outside, so that they cannot be gripped and turned, with the nuts inside; to secure the hasps or bolts, and the hinges..
Fit hinge bolts to both doors. I made mine by turning off the heads of substantial woodscrews, and used a drill chuck to fit them (2 per door ) to the back edge of the door, so that about 12 – 15 mm protruded. Trying to close the door marked the post where a hole needed to be drilled, to accept the hinge bolt.
In this way, once the door is closed, driving out the hinge pins still will not allow the door to be lifted out (My door is actually a fire door with a 6 lever lock! )
With regard to windows, my shop has no windows, allowing full length shelves.to be fitted, to maximise storage space, My shelves had been the bargeboards for a neighbour's house, so can carry the weight of what is placed on them..
It might be a good idea to have internal removeable shutters for the windows, so that when the shop is shut, prying eyes cannot see what is inside to be stolen!
HTH
Howard