RE: Item Category on Item page
The closest feature you have with standard functionality is item attributes.
Where you have a hierarchical category structure, create an attribute with the same name for each level of the category hierarchy and assign each attribute to the category.
When you assign a category that is for example the 3rd level of the hierarchy, the item will pick up the attribute of each level of the category structure. You now have all three levels assigned to the item.
In the items list, you can now filter items by attribute and filter by any level of the category hierarchy as the item has attributes for every level.
You can see attributes in the fact box but not directly on the list view without customisation.
This works seamlessly. The only limitations are if for example you want to use MRP and filter planning by attributes as you can’t do that. But if you just want to manage list views, it solves your problem.