Peaceful cave too good to be true?
As said in comments you are doing it right.

With this strategy, you lose the ability to access any quest reward of level 8 or above, unless you are keeping two weaponned dwarves.  This is a significant disavantage, since you can't get the cheap dwelling, a cow, sow, breed, or place pastures/tunnels/rooms/fields.

As with any food engine, it makes the game easier, but I find the flexibility of dropping the single tiles too much to give up for my tastes.