Being a project manager can be hard, and the most critical question would be how to coordinate the project, let everyone on the same page, and with clear milestone goals. You need to trust your members, and leave the detail to themself as long they are being responsible and deliver high quality work on schedule. The game is no more than the combined work of each individual in the team. So does whether the game succeed, so never let mediocre content escaped.
The game deign document should be clear and to the point, more specifically, to each individual. Give them the big picture, telling them exactly where the quality line reside. And assign clear work directly to each individual.
As for the team communication, and progress update. The service I choose is slack and trello. In slack, I set individual channels for members to write whatever in their mind, as well as content coordinating. The advantage about slack is that you can even set up unity and trello integration directly into the discussion.
In our slack, I stetted up unity cloud build service, so everyone could see what’s going on in the new build and download it to test directly. As for trello, it allows everyone to know the exact spot of where the game is and what is every team member doing.
Two more things about team coordinating worth mentioning is to have clear rule about what each channel is meant for. For example, art channel means only work related to visual asset sits here. Do not let any irrelevant information mixed within those channels.
Another thing is the in-person, or directly communication. In my eye, although the modern technology could in keep communication happened in anywhere in the world. However, the direct communication is where the new idea springs. New idea springs the most when people are debating, playing and testing. Let them meet in-person or on the phone once in a while regularly. You’ll be amazed by some innovational sparks that could have a long influence to your game.