Size and Weight:
First things first: the dinosaur most people know as Microceratops received a name change in 2008, to the slightly less snazzy Microceratus. The reason is that (unbeknownst to the dinosaur paleontology community) the name Microceratops had already been assigned to a genus of wasp, and the classification rules say that no two creatures, no matter how different, can have the same genus name.
Whatever you choose to call it, the 20-pound Microceratops was almost certainly the smallest ceratopsian that ever lived, outweighed even by the middle Cretaceous Psittacosaurus, which lay at the root of the ceratopsian family tree. Remarkably, just like its distant ancestor, Microceratops seems to have walked on two legs--that, and its unusually tiny frill, making it a far cry from "normal" ceratopsians like Triceratops and Styracosaurus. (You should bear in mind, though, that Microceratops was "diagnosed" based on very limited fossil remains, so there's still a lot we don't know about this dinosaur.)