Yes it's going to be weird seeing someone else in the managers seat in the dugout. No Fergie prowling the touchline waving his watch about. Very strange but, life goes on and so must Man United. The best manager of all time in my honest opinion. The haters will argue at the 2 European cups (only 2 - what some mangers in the current game would give for one) but, that detracts from his incredible achievements overall.
Be very interesting to see who comes in now. It will need a big personality to step in to his shoes and not be cowed by the immense presence of him looking down. Mourinho on that basis would be a good fit as his arrogance and ability would almost make him a shoe in. However, I also don't see him fitting in with Man United's profile regardless of how much Fergie likes him but, that said, I wouldn't be surprised to him there either.
Moyes would be another strong candidate but, does he have the star quality to attract the best players either established or potentially to come to the club?
You would imagine Fergie's decision has been made for some time and the manager in waiting has already been earmarked and possibly pre-contracted already, so I suspect the unveiling will be quite soon after the end of the season.