How do you start homeschooling in middle school. We haven't quite given up on b&m school, but...

Any idea on where to begin to even consider if it would work?
How much does it cost, ballpark?
Are homeschool co-ops common and do you need to find a gifted specific one?
How do you handle the classes that are not in your area of training?
Would any online schools work?

What other questions should I even be asking?

Thanks in advance.