There's a limit category for "Player inventory items" -- "Total number of items in a player's inventory."
Playfab's overall terminology and structure of the limits would suggest to me that there should be a limit for "Character inventory items". Since there is none, I have to assume you mean for the Player Inventory Items limit to apply to sum(player,characters...).
If that's the case, can you please explain it better in the limits UI/tooltips? Otherwise can you set me straight?