As mentioned cocaine is often cut with some pretty toxic substances. There will definitely be damage to the mucosal linings of the nostrils.
Don't worry about what you can't do anything about. Do what you CAN do now and stop, like Krissy said. I can say for pretty sure that if you continue to use 2 grams a week you will have problems down the track.
That's a hard question to answer. Blow is cut with so much sh!t. It deff wasn't good for the mind and body that's for sure. But you can heal! Stop taking it ASAP and you will heal!