Astronomers estimate that there are 200-400 billion stars in the Milky Way Galaxy. We can´t actually count (or even see) all the stars in the galaxy, but we can estimate it by calculating the mass of the galaxy (based on the speed that it rotates) and dividing that by the average mass of a star.

Is it true that if you go into a black hole, you can still come out? No. The force of gravity in a black hole is so strong that even light can´t escape out of it...and nor can you. Furthermore, if you go in a black hole you will be dead. As you get close to the center of the black hole, the force of gravity will be much stronger on the part of your body closest to the black hole than on the part of your body farthest from the black hole. As a result, your body will get stretched out until it snaps in half, a process astronomers call "spaghettification". A few physicists think that some black holes could theoretically be less destructive and wouldn't actually tear you apart. In that case it could be possible to come out of a black hole if it connected to a wormhole, which is a theoretical tunnel through spacetime.

Say you headed toward a typical black hole feet first. The gravitational field near a black hole is very strong, and it gets stronger as you get closer to it. This means that the black hole would pull on your feet more than it would pull on your head. In fact, the difference between the force of gravity on your feet and the force of gravity on your head is so big that you would literally be torn apart. You wouldn't survive going into a black hole.

It is estimated that there are 300,000,000,000 or 300 Billion stars in the Milky Way, our galaxy.

This is an interesting question. I found good information to answer to your question on the link below. Astronomers estimate that there are 200 billion to 400 billion stars contained within the Milky Way, which is the galaxy where we live in. However, they also know that there are about 5,800 to 8,000 stars visible from Earth.

First question: our galaxy has between a hundred billion and a trillion stars.

Second question: the classical theory of general relativity drafted by Einstein, which is the best theory we have right now that describes black holes, says that you cannot come out, ever. Einstein's theory doesn't work well with quantum mechanics, however, and is very probably incomplete, which means that real black holes may have some properties that would surprise us.