Can I update my inventory from a CSV file?

Yes, you can. WP-Lister for Amazon currently supports these CSV import plugins:

http://www.woothemes.com/products/product-csv-import-suite/ (paid)
https://github.com/dgrundel/woo-product-importer (free)
https://docs.woocommerce.com/document/product-csv-importer-exporter/ (free)
http://wordpress.org/plugins/wp-all-import/ (free)

Updating an existing product from a CSV file will be very much like updating the product manually in WooCommerce: The listing will be marked as changed and a new listing data feed will be generated. 

Can I import Amazon specific fields like listing title, start price or condition description from CSV as well?

WP-Lister uses  the following custom meta fields to store the information you see in the “Amazon options” box on the edit product page:

_amazon_bullet_point1
_amazon_bullet_point2
_amazon_bullet_point3
_amazon_bullet_point4
_amazon_bullet_point5
_amazon_condition_note
_amazon_condition_type
_amazon_generic_keywords1
_amazon_generic_keywords2
_amazon_generic_keywords3
_amazon_generic_keywords4
_amazon_generic_keywords5
_amazon_id_type
_amazon_maximum_price
_amazon_minimum_price
_amazon_price
_amazon_product_description
_amazon_product_id
_amazon_title

Please refer to the documentation for your CSV import tool of choice for details on how to import custom post meta fields.

For example, if you use the  Product CSV Import Suite by WooThemes, according to their documentation you'll have to prefix custom meta fields with "meta:", so to import UPCs/EANs from a CSV file you would use the following column header:

meta:_amazon_product_id

Exporting Orders

When WP-Lister for Amazon creates an order in WooCommerce, it stores the Amazon Order ID in a custom meta field called _wpla_amazon_order_id.

If you export this column, you'll have the order ID information for each order which will allow you to filter all Amazon sales in a spreadsheet application for example.