I think that the population limit is the point at which migrant waves stop.  So with a limit of 20, you should get enough waves to push you over 20, and then they should stop.

The wiki says:

I don't care how much food it takes for my cook to gain skill.  I just want it to happen faster.  With that as the goal, are easy meals still the best way to go?

I want to sell prepared food to the caravans.

1.  Will the food rot while sitting at the depot waiting to be traded?

2.  Is there some way to find prepared meals on the depot-loading screen, other than through the list of everything?  Prepared meals don't seem to fit in any of the listed categories.

Is there a way to turn off messages for masterful works, especially engravers?

Sounds like there's some disagreement on that one.  In an older version, I recall that nothing could break down a bridge in the up position.  Is that still true?

And when one of these building destroyers does its pathing, does it plow right through buildings, or does it try to go around?

Are there any creatures in the current version that can break down doors, grates, walls, etc.  And if so, which things are breakable?

I've got a soldier who about once a month generates the message that he can't drink because he's unconscious.  I assume he's just a drunk.

In avoiding cave-ins, do staircases count as supports?

As I understand it, you can do five things with plants:
eat them,
cook them,
brew them,
thresh them (at the farmer's workshop), or
mill them.

Cooking destroys seeds.  Everything else leaves seeds.

On the fertilizer, I have no idea.  The current game balance already seems to produce lots and lots of food.

Also check what's in his hands.  I switched my first legendary wrestler over to axe use, and he spent two years off duty as a novice.  Then I realized that he was carrying his axe in his right hand AND a buckler in his right hand.  So he wasn't getting an use out of either.  I made him drop everything, and now he's doing fine.  Since then I've tried to be very careful in watching what my soldiers are carrying.

1)  If water falls down from a higher level onto a floor grate, does it make mist?

2) If I dig a deep, deep hole, only one tile wide, and use it as a garbage dump, will any dwarves fall down the deep garbage pit?

3) If I build a floor grate across the deep garbage pit to keep my dwarves from falling too far, then will the grate catch the garbage, or will the garbage fall through the grate?