Andy, you're not getting ahead of yourself at all - good to think about these things well in advance....and given this is Scotland, who knows when winter will arrive

it all depends on how cold this year is likely to be. we have 5 or so hives in our wee village, 4 of them had insulation put in the roof space (above their fondant feed) and those that did, were up and raring to go much earlier in the year than those that weren't....might just be coincidence but think there is something in it if you ask me.
All we did was cut squares of polystyrene (old fish boxes actually) - 2 joined together and that was all. also we had ventilated floors so there was plenty of roof for fresh air and evaporation.
you also want to close down their entrance and make sure your frames are facing the entrance to keep the heat in as well - it's called 'warm way' funnily enough.
other than that, i dont know of anything else to do.
we were -20 for quite a bit of the winter and our girls did survive, so makes me think this was adequate for where we are....but then who knows what this winter will bring....
oh and one of our mentors who has kept bees for several hundred years (!) told us that she'd used insulation for the first time this winter and she didnt lose a single colony - her first time ever apparently...so that's pretty sound 'evidence' eh?