S you can go by using the existing DB by taking the backup of all the CRM databases.
But there will be two issues related to this:
If you want to create a new instance with the existing db its not possible as it CRM tries to creates a new config db which is not possible to have.
Second if u try to import and go for using the existing deployment and use the existing db then it will create a new Org but meanwhile it will also import all the exsiting org into ur Instance.
It suggest you to take a backup and go for a new DB Server and use the Deployment manager to deploy it.
By which you first have to create a dummy org first and then go for the actual org name by giving the restored db name.
This is how it will work if u want to make the things without getting disturb.
Hope this may help you.
