for the \"boxes\" on the track guards I\'d use plasticard, mouth on the side and the paws would be green stuff of white stuff if it were my call.
Its hard to determine how you want the face in the front to look but if it is like I imagine it id recommend building up a basic(and i mean really rough) shape in plasticard and/or sprue bits.
Is the part on the roof supposed to be a cauldron of some sorts?
Oh! And welcome to the forums!