Are all of the columns required?
No.
If there are multiple items in an order, what is the 'item name'?
Create a different line for each item with the same Order Number.
What units are expected in the weight field?
Kgs.
Can you please supply a valid list of values for the shipping method field?
You can add anything you want in the shipping method field. You can define which shipping method matches with which courier product code by going to Settings > Rules.