How many teams can you have In the latest version at any one time?

There are multiple league formats all with various numbers of teams. In sandbox or multiplayer mode you can set any number of the teams to human controlled. In career it's just one.

So If I start with modern day 32 teams 17 games can I add more teams to the league or no?

Yes in between seasons you would change the league format to one of the larger versions and expand that way.