Customs duty

[bam]

I am planning to start a DtoC business in Japan for K18/K14 jewelry.
However I don't have any experience of buying from overseas, so I don't know much about customs.

We want to make it easy and convenient for customers to buy from us, even if it's their first time to buy from an international site.
For example, we want to include shipping and customs in the price, so that our shop can process the payment of customs fees and other charges in advance. Do, etc. (If possible.)

Question 1.
If I put in the HS code as per the help center below, will my shop customers be able to pay the duty at the same time when they pay...?
https://help.shopify.com/en/manual/products/duties

Question 2.
Is it possible for the shop to pay the duty on behalf of the customer? (I'll include it in the price of the product and my shop will pay for it instead of the state not charging the customer.)

Question 3.
How do you guys do it? What apps do you use? Doesn't the departure rate increase when the tariffs appear on the last settlement page?
I guess it's okay if you don't do anything in particular about tariffs and just show the tariffs on the last settlement page ? As long as there are no problems, that's fine.
Both our customers and our shops want to simplify their operations.

Best regards,