Add the ability for players to create more recipes. Maybe instead of a in game window, Use a manually edited config file or an external program to edit the config file.
Example. Copper from scrap copper. you omitted this one when you added Scrap iron to Iron.
Make it required that if the recipe only requires 1 type in and 1 type out, use the Better Assembler 1
If it has 2 in and 1 out, Then Assembler 2,
2 or more in or 2 or more out, Assembler 3 etc...