4.1) According to http://www.giantvirus.org/top.html, the largest sequenced viral genome is of Megavirus chilensis. It is 1259197 base pairs in length. This is longer than the prokaryote Nanoarchaeum equtans, which has a genome 491000 base pairs in length, according to http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/chroms-genes-prots/genomes.html.
4.2) virus with a double-stranded circular DNA genome: Papillomavirus (Papillomaviridae), Polyomavirus (Polyomaviridae); virus with a single stranded linear DNA genome: Rudiviridae, Adenoviridae; a single-stranded + sense RNA genome: Picornaviridae, Flaviviridae; a single-stranded - sense RNA genome: Arenaviridae, Orthomyxoviridae
4.3) most common serotype of influenza in the USA during the 2010-2011 season: the most commonly reported serotype of influenza was influenza A H3N2 and H1N1, but influenza B circulated as well