Complex 1.21+ Custom Armor system? [advance help required ;o;]

Hello there! I want to create a complex diving suit system (for a underwater submarine) and i saw a cool implementation of such in a mod. But i want to make it Vanilla. I want to know a few things:


    

  1. Is there any available free resource pack templates showcasing new features for 1.21.4?
    2. 

  2. Is there a way to have a different model for an armor piece when it's held/wore/in the inventory?
    3. 

  3. Is there something else I need to know?
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  4. Additional tips since you're nice ^-^
    5. 



What system I saw is:
Player has a "hazmat suit" in their inventory, representing a chestplate piece. Once put into a chest slot, it extends to fill the other amour slots with the same hazmat suit but different pieces (Helmet, leggings, boots). You can take it off ONLY by the chestplate (that's easy, just an invisible curse of binding on other pieces of armor than a chestplate), and, when taken off, it just removes other armor pieces from slots, leaving only chestplate item in your cursor slot.
I also want to ask if it's possible to rename/retexture it if it's folded into one item instead of four? Like, the thing folds from four pieces to one upon taking it off and acts as one item, even fi it takes 4 slots upon wearing it.


Thanks beforehand! 💛
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