Easier to make custom blocks with recipes

You could select either Storage or Crafting when making a Gui.

When you make a Crafting gui you get an normal input slot, a fuel slot and an normal output slot, and an fuel output slot (just in case.) Then when you made it and bound it to a block, you can make actual recipes (with the recipe feature, and it would show up with the Gui name and the bound block.) instead of having to code them in. For input slots you should be able to apply a filter for either NBT data or actual blocks or items.

For Storage gui, there would be input slots, output slots and combi (both output and input.) slots, and those slots should have custom storage sizes and also filters for NBT or blocks/items.