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Use official WordPress and WooCommerce sources whenever possible.
SSS Payment Gateways
SSS Price Quotes
This plugin from SkyVerge, while not free ($49/year), provides extensive management for custom (and core) WooCommerce Order Statuses, and also allows for custom emails. The SSS Price Quotes plugin makes extensive use of the features available with this plugin, and includes some customized email templates that work with it.
This plugin from WP Desk is free (but consider the Pro version), provides customizable fields for order address (billing and shipping), and general order fields. The SSS Price Quotes plugin supports ‘order’ fields ‘order_po_number’ and ‘order_job_number’ on the form_pay (Place Order) page to place them on the same line via the ‘sss_form_pay_fields’ filter at a low-priority, so it is easy for your developer to override and/or extend the displays. It also supports updating these fields, and the core ‘order_comments’ field, by hooking the ‘woocommerce_before_pay_action’ action.