Assuming you aren't using any specific colours in the name, the following code could look something like this:
File path: .minecraft/resourcepacks/PACKNAME/assets/minecraft/mcpatcher/mob
Put all your files in that folder listed above.
Name your properties file as 'wandering_trader.properties'
And name the png file as 'wandering_trader2.png'
I don't know how the model part of the code works, but I know how to assign the properties file to your entity.
I hope this helps!
Have a nice day!