Yes, we will generate some content and then check if it's what we want.
It's gonna be a 45 day project, so we don't expect many conflicts but they can be discussed with the whole team to reach a decision. We aim to create a game with this project, rather than create pieces of a future game.
Yes, a character interaction system that can be exported to other projects would be nice, but the focus would be on finishing the project on time.
We will definitely require some tests as you said and some of the decisions you mentioned are already decided (i.e. we went with the top down perspective)