A really good addition to the game would be "training squads", where an experienced player can volunteer to be the leader of a group of newer players, and go through missions as a way to improve their skills.
This could start with coop training on fundamentals and simple exercises to learn the basics, and have all other modes available for training on general gameplay skills.
Everyone gets rated by their teammates at the end for their work, and offer some bonus XP and preference to leaders who are highly rated by those who learn with them. The goal here should be rewarding and raising the profile of good teachers, and giving players incentives to helping other players get better.
This would allow you guys to avoid needing to make training videos or other fixed materials that will get out of date quickly, give players more ways to learn the game together in actual gameplay, and allow an intermediate setting between random pick up games and full blown competitive.