1)Does defragmenting the HDD (mechanical) after copying/deleting a big file like games/hd movies cause any damage?Frequent defragmenting? "Damage" is a difficult word to evaluate. How about "wear"?
Any use of a hard drive is going to cause some wear, just as driving your car does. But I don't think it is useful to regard this as "damaging" or "to be avoided".
Hard drives have an intended purpose and you shouldn't shy away from using them for that purpose.
I have known people who defragmented daily with no ill effects. I just use the default Windows schedule of weekly.
2)Windows 7 Defragmentor is good enough to defragment a mechanical HDD?
Yes. The obsessive will tell you to use a third party tool.
3)Does frequent shutdown,startup and restart cause damage to any components? What is "frequent"? 5 times an hour? 5 times a day? 5 times a week?
Power cycling causes some wear, but again you shouldn't obsess over it. I'd think most people would say that shutting down 2 or 3 times a day is not excessive, given the average usage pattern.
4)Should I update drivers
,bios if the older one is working perfectly? No.
5)"Leaving a typical system ON for a full day" does any impact?(Nevermind for current bill) Yes, some impact. You are that much closer to the die date, just like a human body.
6)Does copying/deleting files frequently cause any damage to the HDD? Some wear. But that's what HDDs are intended for. Don't obsess.
If there is any other tips for preserving the system components for long life,then tell if possible.(only Processor,motherboard,ram,graphics card,hard disk). Get a good power supply and hope you are connected to a reliable source of power.
Some would point you to a UPS.
Keep temperatures within design limits.
Other than that, just normal maintenance and common sense. Don't hose your PC down with water, etc.