The plains are nasty.

As for metal, I admit I resorted to light cheating. :) I started a new world and logged into it with my character with his metal and left it there. Logged back into my original world, teleported home, then went to the new world to retrieve my metal. For copper it's not really that needed but for iron, transporting metal seemed more problematic.
For the trader, I found a website that will show his spawn points when you input the world seed. I hated wandering for hours looking for him.

Birch seeds just don't exist. To get fine wood if you've cleaned out the area, you can just create and go to a new world to get more. Personally I just use a boat to find more in my original world.