If you don't care about the quality of the fortress, this is fairly easy. I created a zero-intervention fortress recently and ran it for about a decade before shutting it down out of boredom.
What I did was build a sealed-off fortress with no trade, with the only connection to the outside world being an automated pressure plate - trapdoor retracting bridge mechanism to allow immigrants to get in while keeping sieges and ambushes out. I had a large farm set to grow plump helmets year-round, a large stockpile for holding plump helmets, and a large stockpile for holding plump helmet spawn. I had ten wells dug into an aquifer-fed reservoir, a large communal dining room, a large common bedroom with about 100 beds, and most importantly a small meeting room/statue garden continually full of waterfall-generated mist. And that's it. The secret to keeping this working was the waterfall meeting room, the stacking good feelings from standing in mist all the time offset the penalty for living off nothing but raw plump helmet and water and nobody having their own bedroom or anything.
The only interventions I needed to do to keep the fort running were unpausing it after birth announcements (which there were a lot of, what with all the dwarves having nothing to do) and sieges (which would stand around outside for a while, then get bored and leave). Strange moods inevitably failed, of course, resulting in dead dwarves, but the super happy-making powers of mist kept anyone from tantruming. Production mandates also failed, but with no fortress guard there was no repercussion other than bad feelings for the mayor. The only external noble I had show up was the dungeon master, who seemed pretty cool with the arrangements. Never had a hammerer, or duke/baron/whatever - I suspect with no trade depot I didn't the export requirements.
I abandoned that fortress after a decade when it was obvious nothing would ever change or happen. Too boring. No tantrum spirals, just a hundred happy wet dwarves breeding in a hole in the ground.