I am not a lawyer either... :)
TBH, it really depends on what the laws are. I know here in United States, the city has its own laws, the state has its own laws, and the country has its own laws for doing business. You have to abide by them all. Certain permits you need from state, certain permits from city, and certain permits from country.
My recommendation would be to do a Sole Proprietorship. It is fairly inexpensive, easy to setup, and will have you covered from the legal perspective. There are some permits you'll also have to get.
Good news is: You probably won't have to worry about many permits/other paperwork. Unless you get an office or start hiring people.
There's a reason why United States isn't so small-business friendly. The laws make is quite hard for someone to setup a business.
Also, don't forget to file earnings from your game when you file taxes. :)
P.S: Don't get discouraged from this whole legal thing! Trust me, it'll be all worth it once you start getting good reviews, and when the $ starts coming in. This legal stuff is just so you can be covered.