Is there any additional hosting fees for SQL server?

Well, this is Server dedicated to hosting Microsoft SQL databases and typically incur additional hosting fees.

Is there any provision for the critical computer systems and associated components.

For critical computer systems and associated components there is a facility of the data center.
It generally includes environmental controls (air conditioning, fire suppression, etc.), redundant/backup power supplies, redundant data communications connections and high security.

What is the physical layout of the data center room?

Well, data center can occupy one room of a building, one or more floors, or an entire building. Most of the equipment is often in the form of servers racked up into 19 inch rack cabinets, which are usually placed in single rows forming corridors between them.
Servers differ greatly in size from 1U servers to huge storage silos which occupy many tiles on the floor. This allows people access to the front and rear of each cabinet. Some equipment such as mainframe computers and storage devices are often as big as the racks themselves, and are placed alongside them.

1U represents one rack unit of space. A Rack Unit is 1.75 inches in height (44.49 mm).

There would be great arrangements for Air conditioning of the data center room.

Yes it is, there is need to keep the room cool and also to control the humidity.
Generally, temperature is kept around 20-22 degrees Celsius (about 68-72 degrees Fahrenheit). The primary goal of data center air conditioning systems is to keep the server components at the board level within the manufacturer’s specified temperature/humidity range. This is crucial since electronic equipment in a confined space generates much excess heat, and tends to malfunction if not adequately cooled. Air conditioning systems also help keep humidity within acceptable parameters. The humidity parameters are kept between 35% and 65 % Relative Humidity. Too much humidity and water may begin to condense on internal components; too little and static electricity may damage components.

Is there proper backup power supply in the data center available?

Yes, ofcourse, there is a proper backup power supply in the data center available. Backup power is catered for via one or more uninterruptible power supplies and/or diesel generators.

How you can prevent single points of failure in data center?

To prevent single points of failure, all elements of the electrical systems, including backup system, are typically fully duplicated, and critical servers are connected to both the “A-side” and “B-side” power feeds. This arrangement is often made to achieve N+1 Redundancy in the systems.

I got a chance to visit one of the data center, I was searching for the power cables, there was none.

That may be because the power cables are below the raised flooring made up of 60 cm (2 ft) removable square tiles. These provide a plenum for air to circulate below the floor, as part of the air conditioning system, as well as providing space for power cabling. Data cabling is typically routed through overhead cable trays in modern data centers. Smaller/less expensive data centers without raised flooring may use anti-static tiles for a flooring surface.

Does data centers have elaborate fire prevention and fire extinguishing systems.

There are proper alarming systems. System is designed to spot the slightest sign of particles being given off by hot components, so a potential fire can be investigated and extinguished locally before it takes hold and there is also a system designed to take full-scale action if the fire takes hold. Fire prevention and detection systems are also typically zoned, and high-quality fire-doors and other physical fire-breaks used, so that even if a fire does break out it can be contained and extinguished within a small part of the facility.