No, not at all, all updates will be working on any character as soon as you download the update, you still may experience a few minor glitches, but Bethesda are still battling against them whilst you enjoy the game ;D
there's a high chance that broken quests and items will remain that way if you don't start over
This is somewhat true, if you're having problems getting a certain quest to start don't expect to do it on that character, but aside from that everything should work fine.