So about technologies that we used:
I would start with version control, we used git for it.
For build management, we used Maven.
Then we used Spring framework in combination with Hibernate for ORM database.
For frontend, we used Bootstrap, mainly because of its responsive layout.
We also used Lombok library.
We used Apache tomcat for webserver and JSR-303 for JavaBean validation.

Team cooperation
So we had meeting in beggining of every milestone. On that meeting, we created skeleton for the next milestone together and assigned work to each other. So then we knew who should work on what. We tried to distribute work equily so everyone tries everything.