What are the transformed crew symbolizing?
They're all a bit based on the arts of Okamoto Taro mixed with some unique traits; like Brook based on the screamer, Nami on some Taro statue, Momonosuke (Samurai Dude xD) based on fantasy, since Momo in Japanese means peach xD, and for Chopper I can't remember xD.

The Sunny also is probably based on Taro arts, as the figurehead is a representation of the Sun Tower of Osaka as you can see here: