You must have enough money to cover your trip, it is not possible to work your way around Europe, that sort of thing ended years ago. You can't busk or sell paintings, this counts as work and visitors to any European country are not allowed to work. You may be stopped at immigration and ask about funds, if you can't prove you have money, or they suspect you want to work, you will be denied entry.
You can't just camp or sleep anywhere neither, there are many rules about using camping fires in the countryside, to prevent wildfires. It is also potentially dangerous. Look for official campsites.
DO NOT hitchhike. It is not recommended by the police or by anyone with a couple of brain cells. It is dangerous and in some places illegal.
You need to exercise the same amount of caution and personal security as you would at home.
For a start, a criteria for you being able to enter the Schengen Zone (that's most of Europe) is that you have enough money to support yourself without working, and that you have an onward or round trip plane ticket or the money to buy one. You might be questioned about this on entry to Europe and will need to prove that you have funds.
It is illegal for you to work at all, and this includes busking and selling paintings. If the police in any country catch you doing this, you will be detained and deported back to the States and not allowed to return to Europe for some years.
Wild camping is not allowed in European countries. There is nowhere in the cities where a foreigner can sleep rough without attracting attention. You will need to camp in the countryside, miles from anywhere, and will need to carry all your food and water in addition to camping gear. If you are not in an official camping ground, then cooking food will again bring you to the attention of the authorities.
You won't be allowed into any EU country without a return ticket if you're flying from the USA. Street performing without a license is illegal an will get you arrested real quick.
You need to have a major rethink of your plans.
Good luck. Just note that street performing and selling paintings is not permitted as a tourist.
EDIT. do not arrive on a one way ticket as you will be most likely denied entry.
Are you nuts? Hitching alone is NOT SAFE.
And frankly a young girl out camping alone - even if it were permitted - is only asking for trouble.