First of all please How to use code fences. JSON is hard enough to read already without all the spacing getting messed up.
I am pretty certain that PaperUI cannot handle Units of Measurement in that way. You will have to do it in code. For the “but only if…” section use “a script evaluates to true” and use code along the lines of
(event.itemState < new QuantityType("5.0 W"))
I’m not wholly certain I have everything right with that. You might need to pull in QuantityType to use it like that. Try it and see what happens.