Although we know WP well enough but just having doubt on transferring the EComm User database and map it to WordPress woocommerce. Will it work same user can login with their credential in WordPress too ?

It’s hard to say for sure regarding your custom eCommerce site users, however I can confirm that WooCommerce customers are just WordPress users with a different role and extra metadata (billing/shipping address, etc). They are still users, and can log in with their username/email & password. You can read more about WooCommerce roles here:
https://docs.woocommerce.com/document/roles-capabilities/

We have an extension for importing customers here:
https://woocommerce.com/products/customerorder-csv-import-suite/

So if you are able to export your current users to CSV file and then make sure the file is in the correct format (correct columns, schema, etc) then you could use the extension to import them to the new WP/WooCommerce site.

We’ve not heard back from you in a while, so I’m marking this thread as resolved. Hopefully, the above info was useful!

If you have further questions, please feel free to open a new topic.

Thanks.