Use most (all?) of the Lifepaths of Man as is. Add in appropriate lifepaths from the Magic Burner to cover the various magical disciplines.
Elves are made with the standard Elven Lifepaths from the Character Burner.
Citadel Setting
Wilderlands Setting
Create these with the Monster Burner.
Create these with the Monster Burner.
Magic is very similar to Elven Spellsongs.
Consider using Roden instead of Goblins, or adapt the Roden lifepaths for use as Goblins.
Test creation of Gobbers with the Monster Burner:
Most weapons are the default Burning Wheel weapons. Tweak/create the various firearms. Make sure they don't overpower everything else, but have their place. Also take into account the high cost of ammunition for Resources tests.
Create with the Monster Burner. Take into account the different size levels of the 'Jacks and how they will all interact with each other. Collosals have white strength, large working Steam Jacks have Gray Strength, smaller, faster Warjacks have high black strength? Consider creating generic Steamjacks and Warjacks at different size levels, and then specific models can be slight variations from them, if needed at all.
Consider the Enchanting chapter for Mechanika and similar. Or maybe just have appropriate Sorcerer spells.
Take into account the various magical specialities in the Iron Kingdoms. There is clerical magic but healing is difficult and painful, there are the various races' inborn magic (Ogrun and Elf), there are Gun Mages, Warcasters, and just general spell casters. Use as many of the pre-made magical schools from the Magic Burner as possible. Try to keep things simplified so there aren't too many different kinds of magic to have to deal with.
Use Gifted as normal. By the rules as written, only humans can get the Gifted Trait. See if the Iron Kingdoms fiction requires other races to be able to use such a trait.
Warcasting and Gun Magery are just school specializations within standard sorcery. If that doesn't work, use a Magic Burner magic style.
Check to see if Druidism is better represented by Faith or Sorcery. Possibly a Magic Burner school.
Maybe only basic levels of Sorcery are available unless you attend a College of Magic. This could be easily represented with Lifepaths.
Maybe use the Gifted chapter as is? It might be too complicated for its own good and should be folded into another Magic School.
Abstraction and Distillation? Might be too complicated, at least at first.
Trolkin Magic is very similar to Elven Spellsongs. Consider adapting them.
See if the Iron Kingdoms fiction supports Elven Spellsongs or if they should have regular Sorcery.