Where I can request a new tag?
I tried to post a question on "Musical Practice and Performance" and I have found out that it is very short on tags. It's a feature request to add more tags on that site.
Since Music is a beta site, you can create tags yourself once you reach 150 reputation (once out of beta, the rep required goes up to between 300 and 1500, depending on the site).
If your post could do with more tags, people that already have reached that level generally will retag your questions for you.