Hi Sujith,
You are in the correct forum, as you are looking for a CCTV installer, you should choose the best in your area, at present some features you should consider while choosing the one.
Is that CCTV Surveillance camera system can be integrated with your smartphone to allow remote viewing.
IP Security Cameras
License Plates Recognition Cameras
Most Megapixel security cameras require a network video recorder (NVR) to record and manage multiple cameras.
you can have much about them on web.
Hi Zekkie,
Going for a 5omm lens is a good idea, the first thing about them is they are cheap, if you are going for F 1.8, it's nice as the aperture is wide enough for most uses & you may even find yourself closing that up at times.
Second good thing about them is the Field of Vision is very Close to the Human Eye.
their zooming quality is also good enough and suitable for most purposes except being used for may be sports.
If a 6 ft tall person fills the view you can capture only his head.
However i suggest you to have a demonstration from some professional camera installers.