How to become a well established rapper?

About the YouTube-thing: If you made some bad videos, you can either own them or try to hide them. The latter will make them much more effective if someone ever tries to use them against you. I'd suggest you leave them up, maybe with a light-hearted note about how you can't believe how bad they are. If you ever get big, you know someone's going to pull those old deleted videos out of some archive somewhere and say, "Hey,this is what he doesn't want you to see!".