Can you help me with some TREK 520 disc questions?

1. What range of tires can I run? I was hoping to run from 28mm to 42mm+
2. I heard that the rack that comes with the bike is not a very good one. What rack is recommended for the front and back of the bike?
3. How difficult is it to mount fenders and are there any special fenders that are needed for the bike?
4. On a normal ride, without touring bags, where do you store your lock and what kind of a lock is recommended?
5. Is there a good front handlebar bag that I can use to store maps, cell phone, snacks, etc on rides?
6. Should I go ahead and buy panniers and ride the bike with the panniers attached or take them off when riding the bike as a commuter or to the store?

Sorry, prolly pretty silly questions to most of you long time riders, but things I just don't know any decent details about. My LBS will order about anything and I have this feeling that their recommendations are based a lot on profit margin.

Thanks,
Snow