I've been looking through menus, the FAQ, and online, but can't seem to figure out how to build a hero team.
I just finished chapter 1 and summoned 5 new heroes. However, I'm not seeing any way to assign them to the team I plan to use on a match.
To edit your teams, click on the "Allies" tab on the bottom of the screen. From there, you can select the "Edit Teams" button to pick who will be on a team. The arrows on the left and the right of the four character portraits will allow you to choose between preset teams (as 4 seems to be the maximum number of units you are allowed per battle).
It's worth noting that the same character can be used in multiple teams.