AFAIK, Escoria allows you to use only a portion of its features. However, certain nodes (and their attached scripts) will be mandatory :
- Game node (linking globals/game.scn) because it links your scene do the backend stuff (globalvm, esccompile, etc)
- item.gd script for items/NPCs
Concerning the inventory scene, keep in mind that it is only a container. You can (and you should) modify it to fit your need in terms of graphics, and you are still able to add new nodes as children of the inventory or make it a child of one of your nodes to add new features to it, make it more specific.
Anyway, I am not certain that Escoria's inventory is mandatory ; anyway, you are still able to modify the framework to fit your needs ;)
Of course, if you end up with new, generic features, feel free to give them back to the community with a couple PRs ;)