How do I export files to accountants to include orders with Shopify fees
You can get this from Settings / Payments / View Payouts in the Shopify Admin.
How does the accountant who has full permissions access the view payments screen and download them themselves, without making the store owner do this every month?
Go to Settings / Users and Permissions. If you add your accountant under staff you can give them permissions to only "View Shopify Payments payouts".