If I earn money with " Donate " feature and advertisements ?
If it's going to be a MMO I can foresee you having servers. And that costs money, if you get donations that helps you keep these servers online then you would indeed get +-0 or atleast save some money from a good month for the next bad month. So I don't see any big danger in having donations. If you have ads on your site you would be making money from the ads because the site has a lot of traffic. You wouldn't be making money from the product, but just some side money from the ads. That's why I don't see it as a problem if you have any ads as well.
But as always, these are things that I have no expert knowledge of so I would really urge you to follow Kama's suggestion and talk with a lawyer that knows these things.