Give me your thoughts and feedback on a couple things.
Figuring out background lore and Bad Guy Schemes
The Catacylsm that formed the apocalypse ~80 years ago. I know was a battle of "technology vs. magic". I'm picturing that the big Empire that used to be where the PC's live now was in the "tech" side. Probably a roughly 19th century type culture that disovered a mystical source of energy that let them fuel magitech. Very much thinking like the show Arcane (League of Legends).
The Magic side could have been another empire, but I'm leaning that they opened up something extra-planar, and strange creatures came through and started wrecking stuff.
How that echoes back to modern baddies
The Raiders make sense to be more tech minded. Perhaps even religiously so. They live in the city scavenging tech, after all.
The Encroaching Cult I want to then have more magic or biological bent. Trying to figure out what the nature of their magic is.
I'm thinking giving them an insectoid theme. I want to have dragons or dragon-analog type monsters. I'm also thinking Thulsa Doom and "flesh is stronger than steel". Give them a philosophy of, "human society had their chance and failed. It's time for men to fall and give rise to a new era of [something]." I'm thinking "insects" would be an appropriately creepy and logical thing. Easy enough to understand and not as commonly done.
Outline for opening adventure:
Start in the PC's home village and a sense of going about normal business.
There is an earthquake. Causes a cave in and causes general destruction including busting the spars on the mill, letting the millstone roll away and cause more damage and mayhem. PC's have to go into action to control damages, put out fires, and save lives.
NPC tasks heroes to escort a wagon to a nearby village to get a replacement spar for the mill and various other repair materials.
I need a small encounter/challenge along the way. I'm thinking a bridge over a blasted crevasse (scar from the Great War) was damaged or collapsed completely in the earthquake. Strange dark things in the crevasse.
As they approach their target village, there is a horrendously loud roaring sound. It's an out of control airship which potentially wrecks or upends their cart and then crashes. They will naturally want to investigate.
Trouble is, they are closer to the walls of the Old City where the raiders live than any other settlement. They have a limited time before raiders show up to secure this prize. They have to hurry to gather what they can and get away, or be faced with an overwhelming fight. (If they stand and fight, they will lose. They would be captured, not killed though.)
Inside the airship, they find one or two families who have fled the Sinister Magic Cult that had been experimenting on them. They are all various levels of injured from the crash. They also find a metal spike with a gem and a bunch of wiring or circuitry. It contains a consciousness (effectively a magitech AI) and had been controlling the airship. It can not speak, but has limited telepathic powers.
The spike is clearly valuable, but they will have no clue of what it is or what it can do yet.
For the airship, I think I want to make it biological or biomechanical since it came from the Encroaching Cult. With the idea of them being insect or arthropod themed, a giant bug seems appropriate. It would also be alien and creepy.