import problems

The categories and products are linked by the table hikashop_product_category.
Here is an extract of our documentation about how to assign products to categories during the import:

Finally, you can also have a categories column where you can put a list of categories id or a list of categories namekey. The categories need to be already inserted in HikaShop before.
For example:
product_code,product_name,categories
my_product_1,My first product,"2,13"

This will add one product with 2 categories attached: the category with the id 2 and the one with the id 13. You can find ids of categories on the category listing in the column called ID on the right of the listing.

If you only have one currency on your store, you don't have to fill it. It will be added automatically by the system. Otherwise, as stated in the documentation you can either set the currency code or the currency id in that column and the system will make the conversion automatically if necessary:

In the price_currency_id, instead of the id of the currency you can have the currency code. If the price_currency_id is not specified the main currency of the store will be used.

I really invite you to read our documentation on the import which explains how the system works and gives several examples of how to do it:
www.hikashop.com/en/support/documentation/73.html

No, if the product code already exists, it will be skipped.

Edit the products and change their prices via the interface.
Or you can also build a SQL query to update the prices with phpmyadmin.