New organization using teams looking for best practices and ways to rearrange teams/channels

Our organization recently joined Office 365 and we are implementing Teams across different divisions.  Before it gets too far out of hand with people creating new teams and organizing things without a plan, I'd like to implement some best practices for structuring teams and channels.  If anyone has suggestions, I'd love to hear them.  Is it best to create a team for each division and then groups in that division each have a channel?  

Also... we already have several people who have created separate teams within divisions.  Is there a way to change them from teams to channels and then move them into a team after the fact?  I feel like some of the toothpaste is out of the tube but if I can combine the teams in this way I think we can control it before it's too far gone.