That all sounds right except I’d probably put the MouseButtonDown/OnDragDetect logic on the ItemWidget, as that’s the thing you’re actually doing the drag on.
In the example I linked I used the ItemWidget (or spell widget in my case) as the payload, but that’s not what I would recommend, I did that solely for brevity of the example. The payload can be any UObject, so if I were doing it for reals in a game, I’d make the payload UInventoryItem or whatever as the payload. But it wont hurt to use the widget as the payload, you can also use the string field if you just want to attach some string data, perhaps in the future I can make that field a variant, so it can more or less be any primitive type (string, int, bool…). Int in particular would work really well for inventories.