(If you've ever got a question about where to post things - or anything else - drop me a line. That's what I'm here for!)
As for your idea, I think a lot of that stuff is up to you. Don't worry so much about what other people want to read; write the story that you would most enjoy reading (and writing).
Surround yourself with people who are serious about being writers, and who will tell you, ‘Hey—you can do better than this.’ Who will be critical of your work, but also supportive. And who will not be competitive in a negative way. — Isabel Quintero