Sounds like you've got a good skill set, so start composing. Also start reading about composition, and the more specific questions will begin to arrive. Those questions will lead to more questions and as you go, you'll start to understand more of what you're reading, and also realize that composition is one of those lovely open-ended studies that is never done. You'll get more knowledgable as you go, but there will always be more to learn. So go ahead and plunge in. If you can find a class, great! If not, don't let that stop you from doing what you can do right now. Anything you learn now helps prepare you to learn more in the future. But if you want to learn composing, step one is to start composing, and then let what you are writing direct your next steps.