Hi all,
Not done any more to this recently, have been actually using the computer!
As for the power cable routing... I didn't want them going off to the side, as it wouldn't have been symmetrical, I didn't put them to the front, because it would have been more difficult to connect and disconnect (plus, ideally I'd have wanted a 24-way cable that was about 10cm long - I couldn't find one in white!), and I would have had to cut through the metal motherboard tray, and I couldn't think of a way to make it as neat with the tools that I had at my disposal!
I need a properly-sized bit of perspex to go over the front, and some additional lighting... and a properly placed power switch!