That's one sweet looking KW. You did a fine job. As to the plates, yes, back in the 1970s you needed a plate for every state you ran through.
I agree with JT on the Revell-Monogram kits: they're inexpensive, well detailed for a snap kit, & easy to build. There are a couple of downsides though. The tires are not very good, and if you want to make then a daycab the sleepers are molded with the cabs. There is also no brake details.