You can filter / sort by download count using a extended attribute filter. the data is in the ezbinaryfile table. Filesize on the other hand is not in the table so you'll probably have to create a new datatype that extends ezbinaryfile to be able to sort by / filter by size.
Search for 'filter' on this site or ezpedia, or: http://www.google.com/search?hl=en&client=opera&rls=en&hs=gpI&q=Extended+attribute+filter+ez&btnG=Search