It's generally a good idea to disable all your Trader's jobs temporarily until you're finished dealing with the merchants. That'll let them finish their meetings more quickly. You might want to assign a new trader, to make sure they don't have any other administrative responsibilities (manager, record keeper, stuff like that). If you're worried about not getting the values of what you're trading, just make a shitton of stone crafts and estimate. Be very generous just in case you're wrong. That'll give them the experience to figure out what stuff is worth again.
To remove zones, press x, then use Enter to draw a square as you would making to make the zones. Press x again when you're done.
I've never dealt much with animals beyond butchering and training them, sorry.
Fortress guards are just like your police, basically. They'll beat dwarves who don't appease the nobles, and are generally useless. You want them to be as underequipped as possible just so your "criminal" dwarves who are getting a beating for missing a production deadline aren't killed. They're just there to make nobles happy. What I do is conscript any dwarf with a major injury they're not likely to recover from into the fortress guard, as no one cares whether they're able bodied or not. As long as they fill the ranks, the nobles will be satisfied.
