1: No, that would be Dante. Yarrik was merely the most notable non-Marine hero of the War and the commander of a relatively small Imperial force.
2: A bit over two centuries, assuming access to the life-extending Juvenat treatments, which anyone important enough to actually be a common name certainly does have access to. Using cybernetics and other methods, the oldest person I've heard mention of without resorting to Chaos-based immortality was more than half way into his third century.
3: By the old fluff they did not, with their massive support staff keeping track of the Chapter's knowledge and the entire lot of them fulfilling the 'Psyker' bit. New-fluff GK do make use of Librarians, though I'm not sure to what degree they actually act as historians and record-keepers as opposed to just particularly psychically gifted individuals.