Film holders for Graflok back for Nikon Multiphot

I have a Nikon Multiphot which I have been using a Nikon F3 with for 35 mm
transparencies. I would like to begin using larger format with the system. I
have what I think is a Graflok back for the Multiphot and am not quite sure
what exactly this will allow me to use since I have no praactical large (or
medium) format experience. Feel free to correct any misconceptions I express
below.

I assume that I can use certain film holders such as the Polaroid 545i by
inserting the holder under the focusing panel on top of the Graflok back
(True or False?)


If I use specifically the Polaroid 545i with film such as a 4x5 Fuji
Quickload will the image area be 4x5 or only 31/2 x 41/2 or is that only
true when specifically using Polaroid instant 4x5 sheet films?


When reading about film backs, I come across the term "International
Standard" back. Exactly what does this mean and how can I tell if the Nikon
back I have is consistent with the international standard?


If the Nikon back is consistent with the international standard what types
of film holders are realistically usable with this back? For example, other
formats such as 6x6 cm etc?


Thanks much.