I want to Upgrade existing magento website with around 3000 products from magento 1.8.1.0 to magento 2.0.
Note : Design is custom.
Magento did bring out a migration tool to transfer items from magento 1 to magento 2. http://devdocs.magento.com/guides/v2.0/migration/migration-tool.html.
You should be able to download the migration tool from here: http://packages.magento.com/#magento/data-migration-tool
Just note the migration tool is still in beta as is magento 2 but good luck!