In washington state a party is in contempt for something as simple as not making it to the pickup and drop off.  Yes, you can file for contempt of the parenting plan for that.  As I have stated try to lump more than one violation into the contempt motion.  And of course disinterested third parties who can write declarations for you will help.  In king county contempt motions must be served on the other party personally.  I have a section on service of process on my website here.  Ask the Commissioner to give you more than just 14 days so that you have a little extra time to effect service.

In WA child-support and the parenting plan are totally separate.  The duty to comply with the parenting plan is not cancelled because of a failure to pay child support.  The doctrine of unclean hands applies in Washington state as to the second part of your question, however, I rarely see it explicitly referenced.  Essentially, in courts of equity (which the family court is a part of) if one party has done some wrong related on connected to the action complained of the court can deny the relief requested.