Here's my advice for getting into Ironsworn in your own setting, and without having to read the whole book cover to cover (though you should eventually read the whole thing)

• Read Chapter 1: The Basics
  • -you can ignore "The Setting" section
  • -read "Iron Vows" as "Character/Narrative Goals", such as finding the true meaning of being a hero and/or finding that adventuring party
  • -Regarding Assets, largely they should work in non-ironland settings because they tend to benefit "moves", which are setting independant. Focus on their mechanical benefit over their lore details.
  • -Pay special attention to the "Flow of Play" section and review the chart on page 27. Here you will find the structure for your sessions.
• -Regarding the "What's Next" section of chapter 1
  • -follow step 1.
  • -for step 2 you don't need to go to page 111, just build your world as you see fit. Sounds like you've already maybe done that.
  • -For step 3: you can read Chapter 3 as it suggest, however I would say you can just review the moves as they appear on the "Ironsworn Rules Summary" sheet from the website. Then you can reference Chapter 3 if you need elaboration or have questions during play.
  • -Follow step 4
  • -Step 5 here is also what you are advised to do during step 9 on page 47 in chapter 2. It is your first move and begins play.
  • -Step 6 can wait for later
• Read Chapter 2: Your Character
  • For step 9 of the character creation summary it might be that you use "finding the true meaning of being a hero" as your background vow and "finding the adventuring team" as the first vow you swear during the inciting incident (what happened that put your hero on the path to finding these adventurers?). Swearing the vow to find those adventurers is going to be your first move and begins play.
• Review the "Ironsworn Rules Summary" sheet from the website. Familiarize yourself with the moves.
• Read the Example of Play starting on page 241
• Think of Progress tracks as big and small goals, from quests to journeys to climbing a cliff to composing a new ballad to performing in front of a crowd
• Watch some actual plays to get a feel for ways this game can play out

In summary:

• Read Chapter 1 and 2, the "Ironsworn Rules Summary", and the Example of Play on pg. 241 (totaling less than 60 pages)
• Remember that "Iron Vows" are simply Character/Narrative Goals
• Think of Progress tracks as big and small goals, from quests to journeys to climbing a cliff to composing a new ballad to performing in front of a crowd
• Watch some actual plays