To just keep my coins on freebitco.in and to get 4 % is too big risk, how much coins do I need to make some good profit, I need to invest too much and that is a big risk to keep all that coins there.
Sounds like it's not the risk you're concerned about, but rather it's the low return that keeps you from getting interested in this. That's fine. But realize that in the world of investing a low rate = lower risk. So if THIS opportunity is too risky for you, so should every other opportunity that offers you a greater return...aside from simply holding bitcoin.