The networks will send you a 1099 that lists the revenue you've made with them.
You don't have to register an LLC to write off expenses. If you're a sole proprietor, you can write off anything reasonable (definitions vary).
Things to write off include (but are not limited to)...
- advertising expenses
- office supplies
- meals
- percentage of mortgage for home office
- gasoline
- utilities
- services (i.e. CPA)
- vehicle depreciation
Understand that you should run most of this stuff by a trained tax professional. Even CPAs have different definitions of what is a reasonable write-off. Some are milquetoasts and some are cowboys.
One CPA may say, "you want to write off WHAT?!" Another will say "Do it. I'll be there if you get audited."