One thing about this, I must suppose, is that all the living-memory referents for a papal funeral are for cases where the Pope In Office was the one who passed, leaving the RCC under caretaker administration.
Then you have how the only papal funeral since 1978 was that of JP2 in 2005 – and Wojtyla was someone who had served almost 27 years, highly influential in both spiritual and secular-political world issues, respected among fellow high clerics both in his church and outside of it, highly popular among the base. So his passing and funeral were Big Deals beyond the mere ceremonial formality, involving everyone who is anyone wanting a seat in the crowd and with the presence or representation of virtually every prelate of rank in the historic Christian churches.
Like others I expect that for Benedict all the proper formalities and ceremonies will be followed, with the parts related to succession or Sede Vacante skipped, and that in attendance of secular guests you will see a difference of more representatives (Ambassadors and lower-in-the-line royals) as opposed to proper Heads of State/Government or reigning monarchs.
As mentioned earlier he is to be buried in the papal crypt – after all, for 8 years he was the Bishop of Rome, Supreme Pontiff, Sovereign of the Holy See, etc., and everyone in there is a dead former Pope: his main difference is he became former before he became dead.