2. Most animals are not agressive. This includes animals like lions. Alligators, badgers and some stealing animals are exceptions rather than a general rule
3. Only plump helmets produce food directly, other plants must often be processed or cooked before becomming edible. Eggs are good for providing a lot of food, but need to be cooked too. The most important thing to keep in mind is not to cook all the plants of any type or you might run out of seeds. Another useful thing is to get easy to maintain (no grazer) fast breeding animals to rovide some meat now and then. Dogs are actually great for this. Otherwise, just experiment with how much effort you have to put in everything. Learning that is part of the fun. One fort starving because you didn't get enough food, the other one having too much...
7. The term is irrigate. And no there is no automatic way, mostly because you only need to do it once, to make the tiles muddy. From then on, except in some weird cases (using a cheat command to clean all mud, blood and vomit just as an unhappy dwarf destroyed the farm to reveal the mud), everything works fine. There are some suggestions on how to safely irrigate underground stones. However, if you have a soil layer (sand, clay, dirt, loam and some others), this will support a farm without any extra effort
9. One of the first things you should do is make sure you have a raising bridge at your entrance to close your fort in emergencies. After that you can in theory wait any emergency out, with a few exceptions. The easiest way is to set traps. Both weapon traps and cage traps are extremely powerful. Personally I wait with setting anyone to training untill the first migrants arrive, mostly because I can't spare the manpower, also to wait and see if any migrants have military skills.