Answers to a few questions:
1) I've encountered little resistance from using front and rear hubs. There is probably a tiny amount but it's barely perceptible and well compensated for by the smoother transmission and superior gearing range.
2) If I isolate the various mods, I'd say the Alfine hub mod was around £500 in total including labour and materials. It's a lot but worth every penny long-term. I believe the Alfine hub provides more 'bang for buck' than say a Rohloff
3) I'd have to check what the rear spacing was widened to. I do know the Alfine threads were also ground down slightly.
Hi Sesame and Littlepixel I hope you are both keeping well! :-)