In order to see the advantage of being on a team, you either need an active team captain who regularly communicates with you, or you need to know your teammates IRL. For my part as a captain, I try my best to regularly reach out to my teammates, and I make sure to let them know they can contact me about anything. Most of them are friends I knew before I started doing Extra Life, but I've made some new friends along the way too. I try to keep it local, so everyone on my team is at least from the Pittsburgh Area, and that helps too. We even meet up to grab dinner together from time to time. This year I'm even trying to plan some team fundraising events. Every team will be different, and if you're not really feeling welcomed in your current team, or the captain is too inactive for your preferences, just remember that you can always join a different team or even start your own. I sincerely hope you can find a team that you can really get involved in, because the fact that you're seeking more than just a vague association with your team is the mark of a great Extra Lifer!
As for your questions about streaming, I know that the official Extra Life channel often hosts and highlights streamers from the community if you can commit to a weekly time spot to broadcast. The requirements for joining the program should be listed here:
Also, I'm sure @herobyclicking could tell you more!