After doing some more research, and reading the various existing inventory systems, I've concluded that I must make a separate PANEL for EVERY SINGLE SLOT... I REALLY want to be wrong here, but I'm not, even the RPG Template pack has a super-bloated inventory system. So, I'm just posting this to let people know that my question has been answered.

1) Panels and/or Buttons are the only "practical" methods for designing an inventory.
2) C-Script is not suited for this particular project, but it is possible with massive amounts of code.
3) The diablo-like inventory is easier then the Oblivion/Fallout type, but it requires a lot of work either way.

Just incase someone finds a revolutionary new way to do this not implemented in AUM or the RPG template pack, then please let me know.

I hope this helps someone.

-Aaron