Looking for information from tax experts about hobby income

I am writing an article about when hobby income must be declared and when expenses can be deducted for hobbies. I am hoping to get information from a tax professional on: 1. When do you need to pay taxes on money earned from a hobby? 2. At what point is a hobby considered a business? 3. When is it permissible to deduct expenses for a hobby? 4. Can you take the home office deduction for hobby income? Requirements: CPAs, tax lawyers, and other credentialed tax experts.