I would tend to base it on D.F. to start with.
One hero, many hero cards.
Hero cards can be played as followers.
If your hero dies, your followers go home until recruited by a new hero. Their equipment is left in the room that they died in and can be recovered if you return.
Loot is the commodity of choice.
You have one dungeon, if it dies, then game over.
Dungeon dies when all of its vital rooms are conquered.
Vital rooms would be, say, farm, living quarters, and mead hall.
You have a booze stockpile, if it is empty or conquered, then your costs increase or you start losing dwarves.
You could have, say, five cards chosen to start your dungeon(fortress).
you would have your essential places that you lose the game if you lose them.
Also modifier cards, like a caravan would mean you would take a penalty to production, but some of your stuff could exist without being connected to the others. Or you could have underground lumber, or water, or lava, things to define your fortress...
You spend loot to place fortress cards.
Heroes can claim loot from conquered rooms or quests that they play themselves.
Heroes and fortresses would keep separate loot supplies.
Fortresses would have to 'fill' a card with loot when they played it, as a cost.
Fortresses decks have room and item cards.
Room cards have limits, say, a corridor cannot contain production facilities, has limited soldier capacity, but a bonus to traps. A barracks gets a bonus to soldiers but they don't build traps in there. A large room would be generic, could have anything, but doesn't excel, and has a high capacity. A small room might have less capacity but have a more efficient cost due to higher card usage.
Rooms can contain things, like forges, which could improve soldier strength, or tailors, which would mostly produce loot. Or even traps, lots and lots of traps, with a flooding mechanism...
There could be a number of wound tokens applied to heroes, like equipment. If you have a head injury, then it applies a penalty to everything, if you have an arm wound, then you cannot use equipment in that arm, if you have, say, four wound tokens, then you die, and some wounds might count for double... Maybe the wounds could be cards that the fortress player plays, better wounds are more expensive. maybe the wounds need to be played in advance, and the hero may completely avoid the card that the wound is on. I would be tempted to separate the wounds deck and the fortress deck if the wounds were cards that needed to be activated by other cards...
Sooo, I get my six starting cards, soil mushroom farm(provides 1 loot per turn, costs 4 loot to rebuild, one door), Resplendent mead hall(provides 3 loot per turn, costs 30 loot to rebuild, +2 in adjacent rooms, four doors), Cramped living quarters(-1 happiness, 4 to rebuild, 1 door), Decrepit still(+2 booze per turn, 20 booze capacity, 4 to rebuild, 1 door), Lava supply(double cost and production of forges), Drunken oaf(1 power, 1 defence, 1 cunning, free to recruit, when played, place up to one 'Drunken' hero from your legends(dead things) pile on the bottom of your hero deck, if hero, search your hero deck for up to 3 other 'Drunken' heroes and play them as followers).
I put all those card on the field for free:
Lava supply Drunken oaf
smf
Clq Rmh Ds
I then activate their effects. +3+3=6 loot, happiness is at +1, 4 booze. I draw and play my two drunken swordsmen and a drunken fluffy wamble farmer. And I draw cards from my decks, maybe 6 fortress cards and 3 hero cards, and maybe get a bonus 20 loot to build my fortress with. I didn't draw any rooms, so I place a spinning death-blade(6) and two crossbow dwarves(3+3) in my Resplendent mead hall, which lowers its production by one each, and then put a head then torso wound(6) on the spinning death-blade and a head wound(4) on one crossbow-dwarf and a torso wound(3) on the other.
My opponent attacks my fortress with a retired burglar hero and a loyal swordsman follower, the burglar's high cunning bypasses my trap then the units all attack each other, they kill both crossbow-dwarves and the swordsman uses an ability to take the damage, and dies, but my room didn't take any damage so it is still standing and I get to call in more guards next round and attack unless the enemy hero retreats...
Every round you draw up to a certain number of cards and can can choose to discard them if you want to draw more next round?
Soldiers don't have wounds, they just die if they are attacked by a higher strength than their defence?