It's hard to give an exact number as new issues keep coming out. But as of now, there are quite a few series and one-shots featuring the Young Avengers.
I don't know for sure. Maybe you can follow some comic insiders or fan communities on social media to get the latest rumors and speculation about the return of the Young Avengers comics in 2018.
Definitely not. The Avengers comics have a specific set of characters and Yondhu isn't part of that lineup. Maybe you're confusing Yondhu with someone else?