You used a horribly outdated guide. This is why you shouldn't follow video guides, there's no telling how outdated they may be and any time the methods change slightly an entirely new video needs to be made, which most people don't bother doing. Had you been using an up to date guide, you would not have needed to downgrade, and the newer methods are much safer.
You are right about this. A9LH is horribly outdated. But… if it happened two years ago this is not as bad as it sounds:
It's not even the newest method of installing A9LH, that method must have been outdated for something like 5 years now.
That's good news!
You need to flash the flashcart for ntrboot first using a working console
DS is best as it will be compatible with more cards but yep you should be able to use any of the three kinds.
You'll need to find firmware files for your flashcart that will let it run DS games, then you'll be able to run the nds file that flashes it.
No, you just need the kernel files and the ntrboot flasher. And make sure the card is FAT32 formatted.
