Sorry to hear about your AN diagnosis, but welcome to this forum. You'll find a lot of good information here. Sometimes the docs don't have the time to really sit down and tell everything they know about AN. Iin some cases they may not know much, since AN is rare enough that they rarely see an AN patient. You must have lots of concerns and questions, ask away here and do some Internet research.
It sounds like your doc may have said your AN is life threatening. AN can be life threatening if it's pressing on the "wrong" place, but that is very is rarely the case. AN is usually slow growing, the average growth rate is thought to be 2mm per year, so you have time to go through all your options. I would advise not rushing into treatment after only seeing one doctor. Get second and third opinions. Explore the various treatments and their pros and cons until your confident that your're doing the right thing. Make sure that you see doctors that have vast experience threating ANs, and are currently treating them regularly. That usually means going to a regional tertiary teaching hostpital.
On this Forum are several AN patients younger than the average age for diagnosis, we even have a few teenagers.
One thing you may want to do is obtain your own copy of the MRI. They're usually on CD with their own viewer program. Mine where free for the asking.
The loss of vision sound a little scary. A few people on the forum have reported some visual auras before diagnosis, which is usually a precursor to migrain headaches. The coughing fits sound like your AN may be pressing on one of the two facial nerves, this can affect swallowing, etc.
Everyone here knows what it's like receiving an AN diagnosis. It's scary, but as you learn more about it you may not feel as freaked.