the smallest bag i use with the GFX, finder attachment and 32-64 (with hood attached) is
this incase slingbag it fits in sideways, i always have the finder rotating pretty freely, so it just "leans" to one side when i put it in....there is room for batteries and other small stuff, maybe a small lens but the rear compartment (for iPad,....) cant be used anymore, bag won't zip up easily....
they also used to have a much bigger version (could not find it on their website anymore) which holds the same kit plus grip plus lenses and mbp 15"....
i also use my lowepro magnum (s) which i just keep coming back to...
for hiking i use
Mindshift i believe i have the 25L, these are really, really good backpacks and ridiculously light.....the GFX, zoom, grip, with finder attachment fits right into the lower/camera compartment.....i hate having to take off my bag(s) or having to put the camera together to shoot, so these options all let you shoot fast....
after looking at the mindshift site a little more
this one looks really good...compact, light but still big enough and maybe better then the incase option....