Hi,
1. First, there are several options to hide the price display on products listings and the product pages. The "show prices" option can be found in the Display tab of the configuration for the product page and in each one of your menus/modules via the menus Display->Content menus/modules.
Then, for the checkout, invoices, order info, you will have to edit the corresponding views via the menu Display->Views. For the checkout, it's the file cart of the view checkout. For the invoices and order, it's the files invoices and show of the view order.
For the emails, if you have the Business edition, you can edit them via the menu System->Emails, otherwise, you can edit the files in the folder media/com_hikashop/mail
2. The best is to create a hikashop plugin and implement the onAfterOrderCreate event.
You can look at the other hikashop plugins files for examples. They are in the folder plugins/hikashop
We have some documentation on that here:
www.hikashop.com/en/support/documentatio...r-documentation.html