At this point it might just be easier for you to send over what you've got, and I'll create a quick corrugated normal map that you could use as a learning example. Let me know if that's an idea that you're amenable to!
Tiling is a matter of understanding how tiles function. There's tons of video content out there explaining how to make a tileable texture, but probably not as many for NDO. You need to define how many repetitions you want within the tile: essentially, how many corrugated pieces of metal need to be within your texture. To…