Hmmm. I'm not sure if there is a limit to how many are able to be hooked up to pull something. I know that currently there are a few carriages or boats that have like 2-4 pulling. So it could be possible for more. Not sure about the limit to that. Would definitely be interesting.
As for the second question, I really don't know if that's possible, it'd be an awesome question for a dev. Maybe you'd hook them up to your horse like a guide?