I would make a PanelContainer and if you intend to have many different backgrounds a TextureRect, then a TextureRect as a child for the Item image (Full rect, scale ignore size and keep aspect centered). The various decorations in the corners i.e favorite, customizeable, crafted before, and in-storage can be TextureRects children anchored to each corner; for multiple in a corner make use of HBoxContainer. Set a minimum size for the root node.
Here’s my scene tree, and ugly make shift images + emojis.