You don't necessarily need to file official paperwork, but it's not a bad idea to get a business license. You might also want to consider opening a business bank account For someone like you, you will probably not have any problems if you don't, but there is one important consideration for tax purposes.
You must report ALL income from all sources for income tax purposes. This includes any income as a photographer / journalist.
As a business owner, you will be able to deduct any legitimate business expenses you may have. When you file your taxes, any deductions you claim will offset any income and you will only have to pay taxes on the difference. You may even be able to claim a loss and deduct that from your personal income. (Be warned, however, that the IRS frowns on businesses that don't make a profit for more than 2 years out of every 5. You eventually have to show a profit.)
If the IRS decides that you are not a business, you could be declared a hobby. That means that they will disallow some or all of your expenses. You will still be required to report your income but you won't be allowed to take deductions.
One of the factors that the IRS uses to determine if you are a business or a hobby is how serious you take your business. If you have a business license and a business checking account, they are more likely to consider you a business. You should also keep accurate records or all income and expenses. There are a lot more considerations, but the bottom line is that you want to be as serious and formal as you can when running your business or you could be penalized by the IRS.
You will have to report your income no matter how you look at it. The more official you are, the more likely the IRS is to allow your deductions. A business license is a deductible expense, so for me the easy answer is "yes." Start an official business. It makes more sense.
Sorry I can't answer all of the questions you have about a photography business, but I can talk about taxes. I teach income tax preparation courses at www.1040taxschool.com so I know about taxes.