Is there any tool like Express migration tool available to migrate from Sitecore 8.2 to Sitecore 9.0? Sitecore 8.2 have MongoDB but on Sitecore 9.0 no mongoDB and we have Xconnect so how the analytics data will do? How feasible is it to go for the migration now and what steps should be important in considering so?
You can find the downloads for the migration/upgrade tools on the Sitecore 9 release page: Sitecore 9.0 Initial Release Downloads
Since you are on 8.2, you can use the 'upgrade' package there.
Specifically for the xDB data, you'll want to look at the xDB data migration tool
If you are on an older version of Sitecore, the express migration tool 3.0 has been updated to migrate users from older versions to 9.0.