The big differences between the KDX250 and the KX250 are transmissions, KDX = wide ratio and KX = close ratio. The KDX also has lower compression ratio, different carb settings, a lighting stator, a completely different chassis including plastics and suspension.
Nothing special to pay attention to on the KDX250 vs any other two stroke.
I have not seen original stickers anywhere as they have long been out of production. You might get lucky and search Ebay for some NOS ones or maybe someone that is reproducing them now.
I haven't restored one but I do have one I wish to rebuild the engine and install the engine in a better chassis. The reason you won't find many KDX250's that have different graphics is that almost no one liked the KDX250 bike due to the excessive weight and it's poor handling characteristics. As you have noticed, they weren't made for very long due to poor sales due to the aforementioned issues.
I really think Kawasaki really screwed up in how they made the KDX250. They took the '89-'90 KX250 engine and really reworked it in to a great enduro/off road engine then saddled it with a chassis that handled like a cow and it felt as heavy as one. If they only would have just dropped it in the regular KX frame with some lights added on they would have had a real winner. It's really a shame.
