If the person who made this wants to be thought of as a professional, they should answer your question on fiber content & washing instructions, regardless of whether you disagreed on other things (unless of course you haven't paid for it, then they have ever right to ignore you).
That said, chances are the inner layers are washable, but in order to err on the safe side I would hand wash and hang dry.
DO NOT EVER put dirty garments in plastic garment bags!!! (well, not for longer than it takes to get home from a con) That is a great way to ruin them. Doing that is pretty much the equivalent of leaving a tuperware with half a sandwich in it in the back seat of your car, it can go nasty in an amazingly short period of time. If the garments are polyester, they can retain funky smells even after washing. Also, dampness from sweat can lead to mildew, which is one of the most permanent stains possible on fabric.