I figured that Moxana's urn-on-wheels was a portable analogue of Polyhymnia's elbow-rest pillar (http://en.wikipedia.org/wiki/Polyhymnia)?

Hadn't noticed the chain on #7 before, but perhaps it's meant to imply an anchor, which would tie in with navigation as suggested by herdsholmferret... it's hard to tell behind Moxana's hat, but it looks like the object held by #7 may have a lower semicircular arc-- could it be a sextant or similar instrument? OTOH, good catch on #7's marching-band hat and color-matching to #1-- now that you mention it, the visual effect of #1's hairstyle inside the instrumental frame does rather resemble a lyre.