Perhaps a mix of both might work. Instead of 8 (for example) fully fleshed out playable Origin characters, perhaps 5 of them and 5-7 "companions" that can be encountered across the game (going on the idea that the latter will only take about half the work to create and implement as the former). Seems like that would solve the problem of knowing every NPC from the beginning, having no surprises to look forward to, and having too little variety for later play-throughs.