user fields

If you change the files via the interface in the menu Display->Views, you won't loose your modifications when you update.

Please provide an image of the different zones of the page and how you would like them to appear on the page so that we can see what you want to do.
Price depends on what you want us to do, so we would need more information to give you a quote.

That's simple enough. I've done it for you as it's just two lines to move in the view file and that the access was still working.

The custom fields information will also be in the email you receive as administrator when the order is created.
Additionally, you can see the custom fields information on the order page on the back end.

That looks like you have a problem in the database structure of HikaShop caused by a problem during the update of HikaShop. Please turn on the debug mode of joomla in the configuration of joomla and do an order again. You should get an error message at the end of the checkout explaining which database problem it is and that we help us tell you what to do to fix the problem.