I live in Brazil and the game is very expensive in this shitty country. So, I would like to know, is it NECESSARY to have premium account to play?
Advantages of premium account
As far as I know there are no premium accounts. You need to pay to get into the game and test it. It's still an alpha, paying insures you get the entire game and all updates.
There are different packages which you can purchase, I purchased the lowest tier, it's really inexpensive. Not sure why you say the game is very expensive?