The base Composite Plating ability doesn't interfere with any Monk class features. However, if you take Mithril Body, Ironwood Body, or Admantine Body, those all change the designation of Composite Plating to a category of armor (light, medium, and heavy respectively).
Best thing you can do as a Warforged Monk is to just save your feats. You keep all of your class features online and have the ability to get armor enhancements without referring to a 3.0 rule.