If you were wondering just how much there was to do in GTA Online, once you've sated your desire for self-created stunts, mayhem, and murdering, it seems there'll be some 700 different missions to complete. That should keep you going for a bloody long time, then.
There'll be at least 700 missions in total, which are continuously renewed, with 500 accessible at any one time. You'll find the missions while roaming the map, or through your in-game phone with non-payable characters doling out jobs. If you're up for a quick hit, though, there'll also apparently be a menu list of missions to quickly pick from and play right from the off.