Requirements vary by county, so I will give you answers based on my experience with my county (Orange). Feel free to correct me anybody if I'm wrong.
1. Yes, you can. Hunter's safety certificate is an acceptable form of "Proof of Competency" and you can get that when you're very young.
2. This may vary percounty. I personally took mine in to the court. Whlie there, they photocopied my drivers' license and "proof of competency" as well as my expired PA CCW permit.
3. I would keep physical features to birthmarks, tattoos, hair/eye color, noticeable scars, etc. It's really at your discretion. I don't know whether they view the amount of depth you give as an indication of your straightforwardness or what.