When is Middle School Chemistry coming out? And is it necessary for high school level(I know the basics)?

I think you should be able to manage with the high school level if you're at least a bit persistent. Middle school chem. would definitely be quite beneficial, though.

I recommend you just go for it and try to do a lesson or two. If it's overwhelming, then I suppose the most you can do is to either find middle school chem. content elsewhere or just wait.