No, you cannot have any kind of physical access to our data centers.
You can choose from the available add-ons/upgrades for your packages for hardware upgrades.
Yes you will have root access to your dedicated server.
Hardware failures are very rare, but they do happen. They are a part of the hosting business. We repair all failed hardware promptly, to minimize any downtime caused by hardware failure.
The control Panel software which comes with your account will take care of new DNS zone creation tasks. You will require you to setup the nameserver once. With Webmin or no control panel option VPS owner will have to manually manage DNS zones.
You are allowed to use unlimited domains.
With Dedicated server you as a user get your own Web server having full control over it as root users.