What are my fortress essentials?

Your fortress really only needs 3 things: Food, Fun, and Fermented Beverages.

Food

Dwarves need to eat to survive (duh!). If there is no supply of food in the fort, dwarves will quickly stop doing any assigned jobs as they attempt to hunt vermin to survive.

Dwarves aren't happy when they're forced to eat vermin. A farm of plump helmets is a good way to stave off hunger indefinitely, as long as you have seeds to plant. If you don't cook plump helmets, they will leave seeds when eaten, allowing infinite sustainability.

Booze

Take a gander at any one of your dwarves' profiles. See that last line? "and needs alcohol to get through the working day". It's that important. Every single one of your dwarves runs on alcohol.

No alcohol means unhappy dwarves who are forced to drink water. If they can't drink water, they'll die of thirst. You cannot rely on your stocks screen alone to determine if you have enough booze, because dwarves have one (and only one) rule of drinking -- you can't drink from the same barrel another dwarf is currently drinking from. You may have 200 units of alcohol in your fort, but if all of it is stored in a single barrel produced by your legendary brewer, you'll lose dwarf after dwarf as the line for the barrel gets longer and longer.

So there's two things to keep in mind for sustaining alcohol levels. First, production, which is easy - simply brew the plump helmets you've been growing to eat -- they are a very versatile mushroom. You'll even get the seeds back.

The other thing you need is enough barrels to store the booze. This usually means wooden barrels from a carpenter, but you can make metal barrels as well at a forge. And, recently, stone pots, from a craftsdwarf workshop fulfill the same function. If you don't have excess stone for as many pots as you need, you're a) not digging down far enough, or b) stuck above an aquifer.

Happiness

If the excrement starts to hit the rotary device and dwarves start dying off, your ability to recover is tied directly to your dwarves' collective happiness. If too many dwarves become severly unhappy, you risk a tantrum spiral that culminates in the death of your fort. I'll simply quote from df.magmawiki 's page on Tantrums:

Dwarf A, a craftsdwarf, gets the urge to build a mysterious construction, but unfortunately there are no 'body parts' or shells to be had.

A goes berserk, kills dwarf B, and wounds dwarf C.

A is then struck down by dwarf H, making an unhappy thought for A's friend dwarf E.

B's loved one dwarf D, and friends E and F, get a strong unhappy thought.

D, going to help C, throws a tantrum.

He kills C in his rage, giving another unhappy thought to C's friend F.

F, now horribly unhappy from the death of two of his friends, throws a tantrum destroying E and D's beds.

E, now very unhappy from two of her friends dying as well as losing her bed, goes melancholy and commits suicide by jumping down the well, giving an unhappy thought for D and J; and contaminating the only water source.

D, despite the happy thought for fighting (and killing) C, is overwhelmed by unhappy thoughts and tantrums again.

This time he destroys a bridge, drowning F in the moat (as it has no ramps), and then punches dwarf G.

F's friends, I and J, both get an unhappy thought.

E's body rots, causing J to tantrum. He punches G, hospitalizing him.

D once again punches someone, this time I - cutting his lip.

Without fresh water, G dies a slow death of dehydration.

I, even more angry due to being punched, punches D back.

D, finally being overwhelmed, goes stark raving mad.

I, angry about being D's punching bag, punches J, and J punches H out of anger.

I, Unable to wash his lip with clean water combined with all of the rotting corpses, succumbs to infection.

D dives into magma, creating a unhappy thought for D's friend, H.

H, in the wake of death and Miasma finally goes berserk and finishes the fortress off.

The more happy thoughts dwarves have, the less they care when their lover / child / bff dies a horrible, horrible death.

Luckily, Dwarves are simple creatures, and it is relatively easy to keep them entertained. The wiki even has a page dedicated to this.

A quick suggestion would be to flood your dining hall with statuary and decorations, give each dwarf a bed of their own, and don't let them go hungry or thirsty.

Well, the things you really need are food, booze, and wood. You can make farms to grow plump helmets, it give you both something for your dwarves to eat and to drink. Wood is needed to make beds and doors for your growing population, and barrels to stock food and drinks. You should also have a well, in case you have injured dwarves or lack booze. That's all you really need.

You should also have some metals (copper, iron, bronze...) to make weapons, in case you get attacked. For this, you need to mine to get ore, and to burn wood or find coal (bituminous or lignite). You also need an anvil, that you either bring with you on embark or trade ASAP. Then you can make armors and weapons, and all kind of metallic furniture too :)

When your population grow, you'll start to get nobles. They will want better rooms, and maybe a private office or dining room. So you'll have to make more furniture for them. They can also make mandates, which means goods of a certain material. If they are not fulfilled, a dwarf will get sentenced to a beating, so you should be ready at any time.

Here's my giant checklist of fortress health questions I like to ask myself periodically. For your question specifically you probably only need the Food and Drink, Happiness, and Defense sections.

• Mining
  • Need to order any exploratory mining? Any new gem deposits you need to mine? Any construction to order?
• Food and Drink
  • How's your food supply? Are you producing more than your dwarves are eating?
  • Plants
    • Do you need to build any new farm plots? Are your farmers keeping your existing plots fully planted? Do you have mills? Are they operating?
  • Meat
    • Any animals ready for slaughter? Any new animals that need to be penned or caged? How are your hunters doing?
  • Drink
    • Are your stills producing? Do you need to craft more rock pots?
  • Eggs, Milk, Cheese
    • Need to build any nest boxes? Need to order animals milked? Need to order cheesemaking?
• Raw materials
  • Wood
    • How's your wood supply? Need to order some chopping?
  • Fuel
    • How is your fuel supply? Need to order new production?
  • Metal
    • Steel
      • How's your supply of steel components? Need to order any smelting?
    • Adamantium
      • How's your adamantium supply? Need to order mining, strand extraction, or wafer smelting?
• Crafting
  • What are you going to sell to the next caravan? Need to cut any gems or order crafts?
• Happiness
  • Check for unhappy dwarves in Dwarf Therapist. How are you going to make them happier? What fortress improvements are you making? Statues? Upgrading furniture? Smoothing and engraving? Check Nobles screen, any new demands?
• Defense
  • Fortifications
    • How are you dealing with invaders? Need to build any new fortifications? Are your cage traps being reset? Need to build more cages?
  • Military
    • Need to make new squads? Adjust schedules? Are squads training? Archers practicing? Spot check equipment, need to order arms and armor crafting?
• Immigration
  • Have any migrants arrived recently? Do you need to adjust their labors or assign them to squads?
  • Housing
    • Do you have enough bedrooms for current and future population? Need to order furniture crafting or bedroom digging?
• Medical
  • Do you have a hospital? Is it big enough? Is it well supplied? Have you assigned the best Chief Medical Dwarf? Do you have enough medical labors enabled?
• Efficiency
  • Are you happy with your fortress layout? Need to make wider hallways or stairs? Need to move or adjust any stockpiles?

Magma. Really, that's the only thing you NEED. Food, Booze, Happiness and Work!? Those just make things run smoother.