Many people use MTTs as their sole income source. There is a very high variance rate and it's suggested to have about 100 buy-ins for the level you plan to play it.

This is all covered in the FAQ, the stickied post at the top of the forum. If you don't find the answers there, the Anthology of 2+2 wisdom thread, which is also stickied at the top of the forum, will have all the answers you're looking for.