How to can I manually update all the drivers. I see my Nvidia card's support software always says new update available. Is it safe to update drivers from Nvidia site, some other sites(for other drivers) or Apple releases special type of drivers for there hardware and only those will be supported?
The important Apple drivers which Windows invariably doesn't have updates for are Facetime camera, Apple keyboard/trackpad/mouse, and the IR receiver.
Beyond these you can update any drivers that MS has to offer through Windows Update, and I've had no issues with downloading video drivers directly from nVidia. Always create a restore point so you can backtrack if you install something that doesn't work as well as it should, link to MS help page here.
To my knowledge there are no special drivers required for Boot Camp Windows. At least for the graphics adapter I did it myself on my Mac Pro without degradation, disruptions, blue screens or similar.
As with installing any low-level software, it is advisable to create a backup beforehand, so that you can roll back, should something not work as planned.
The most important driver upgrade IMO is graphics drivers. My experience with Macbook Pro's of the 2009-2011 vintage hs always been frustrated by the outdated drivers supplied by Apple, and the lack of support from Nvidia.
I have found this solution, not tried it myself Boot Camp: How to get the latest NVIDIA drivers for your Mac
I have upgraded to a Macbookpro with AMD graphics card. AMD now offers support for Bootcamp on Mac. AMD Apple Boot Camp Software Graphics Drivers