HP zbook 15 mobile workstation default memory configuration

[fastKitty]

I have a zbook 15 mobile workstation (i7-4800MQ @2.7GHz).   When I open the expansion panel, there are 2 empty memory slots.   Windoze says there is 8G of memory installed and elsewhere I've read that this device "should" take 32G given the CPU/memory slot configuration.   Sticker under battery gives "official" model as HSTNN-C77C with marketing name HP Zbook 15.   So supposedly that is all correct.

Without taking it apart more, is there any way to know how that 8G is configured?   Would they put two 4G modules in there or a single 8G?

I've read that you should upgrade the RAM to be all the same size for max performance but not sure if that's a hard fast requirement.

Now assuming this is an 8G module, if I added another 8G, would I have to put it on the "inner" socket first or would using one of the easier accessible ones be acceptable?    And is 24G a valid configuration with 3 8G modules if I populated the two outer ones?

But if the 8G is via two 4, am I stuck, without upgrading the internal ones, to putting more 4G RAM modules in?   And would I have to populate both of the outer ones at the same time?