If it says you are missing these items ignore it those do not exist in forge now only in minecraft.net in the creative menu they are all there. Just be cautious of possible lava pools at the bottom of the platform it will set it on fire. If you want to use commands go to the official download page to see more, it is called Custom Trades Mod by supercat765.
Now for custom trades you must do, and I quote.
"Place Items in Chest
top row is first give item
mid row is second give item(Optional)
bottom row is receiving Item
there can be up to 9 trades defined
use "Spawn Custom Villager" Item on or beside chest
remove Chest and trade items
enjoy."
Let me know what I should add or remove also let me know of any bugs I can try to fix.
Also, possibly what other versions this should be in.
Lastly if you want to download this and it is not working, I suggest using the Curse Forge app it is much easier to download and use.