Is this right if on 11.4 or above it will be more difficult? I need a second 3ds or hard mod?
If below I can use Luma3DS?
no. If you have a flashcart it doesn't matter what firmware you have it's easy. if you're below 11.4 ie.. 11.3 or 11.2 you can use soundhax(free method)
If you're on 11.8 you can use seedminer or Frogminer(Frogminer is not on that guide and I haven't used it myself so I don't know how easy it is to do but just search Frogminer)
you need to read the guide several times before you get started specially since you're having trouble understanding the suggestions made here.
https://3ds.hacks.guide/get-started
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Also when you get to the point where it tells you to make a nand backup. DO IT!