We ship overseas for our Ebay business and here's what we have
found. Regular USPS shipping is the most economical because contract
carriers such as Fedex & UPS charge an additional brokerage fee for
physically moving the items through customs. Not only will your
customers have to pay the normal customs charges, the carrier fees
can be a steep and nasty surprise. Packages of less than 4 pounds can
go letter post; packages of more than 4 pounds can go parcel post.
International priority mail is also an option for some weights.
As far as insurance goes, you have a couple of options. Foreign
packages can't be insured unless you send them registered mail (I'm
not sure that this applies to all countries, however). Most sellers
opt to go with private insurers (search shipping insurance on the
web). Some will also allow you to add tracking with these services.
I've never had to use such a service, but did do some research when
we decided to expand our shipping. There are two different custom
forms. It depends on the dollar amount of the item. Some countries
have restrictions on shipping jewelry. I don't think Japan does.
Sometimes we will put 'fashion accessory' on the customs forms when
shipping jewelry and have never had a problem.
Hope that helps,