I want to upgrade my site 1.7 to 2.0.
Is it possible?
If possible then what the issue face of after upgrade?
Yes, you can upgrade your site to Magento 1.7 to Magento 2.0.
But to upgrade site, you need to take care of below steps.
Step #1: For upgradation you need to migrate Magento 1.7 site data to Magento 2.0.
So, for this you need to use Magento 2 default data migration tool. https://devdocs.magento.com/guides/v2.3/migration/migration-tool-install.html
=> You need to install data migration tool and then need to run commands to migrate "Settings","Data" and "Delta" all the commands provided in Magento 2 data migration guide.
Note: Default Magento 2 migration process will not allow to migrate third party tables and data. Also might not be migrate additional columns which are already created in Magento 1.7 databases.
Step #2: You need to upgrade the code / theme as par Magento 2 standard.
After successful migration you can use migrated DB for new Magento 2.0 setup, but you can't use custom modules of Magento 1.7 setups. You need to migrate custom module code and also if you used any third party paid extension that also you need to purchase again as Magento 2 compatible.
Issues Might you face after/during migration:
=> During migration you might face error related to "eav_attribute", "catalog_eav_attribute" tables because of "backend_model" or "source_model" not exist. You can modify into the database. The error is because of third party module model doesn't exist.
=> If your Magento 1 site is live and want to develop Magento 2 store, then might be a change to put your Magento 1 site in maintenance mode while final migration done for Magento 2 setup and site will be live of Magento 2.
Above is the basic information for Magento 1 to Magento 2 migration process. Let me know if you need more information.
Might be above information will help you.