Upgrade Magento 1 to Magento 2 + new design

Hi,

we have Magento 1 website with the following attributes:
1. Multi domains - we have several catalogs on the same servers, each domain access another catalog.
2. Customized search - search by catalog number is very important to us. Therefore we have customized the search to improve search results.
3. Immediate appearance of new item on website. We have purchased an add-on that immediately indexes and show new products that are uploaded to the website.
4. Catalog items and website users are being uploaded via API that we built.
5. User searches are being recorded to another server using a call to an external API.
6. Various other customizations that will be explained later on.

Project scope:
1. Upgrade the existing website to Magento 2.
2. Apply new, mobile friendly design, that we will provide later on.

Please let me know the following:
1. You have experience in upgrading Magento 1 to Magento 2.
2. How would you estimate the amount of hours required to perform upgrade to Magento 2.