1. How can I manage inventory for assigned products?

It depends on your inventory source of truth:

• If you manage inventory in BigCommerce, you need to update stock for assigned products right within BackOrder app. It can be updated individually or in mass by importing a CSV file.
• If you manage inventory via BackOrder API, the product stock will be updated automatically and periodically within your API setup. If you update inventory in BigCommerce for BackOrder products, those updates will NOT be reflected in the app. If you update inventory in Backorder app, those updates will eventually be overwritten by the API connection.
• If you manage inventory in ERP, the inventory can be managed in BigCommerce. Any changes regarding inventory level in BigCommerce will be pushed to Backorder automatically.