Personally, I don't think it's a good idea to have Races as factions.. setting it after Oblivion could work, but I for one haven't played it, and so I know nothing of the games' events or ending. Aye, I'm a purist. Shock horror. If you do a Tamriel wide map, I'd say start it after Cuhlecain's assassination (2E 855-3E 200, 241 years in total, mebbe). Plenty of conflict.