Yes, the iPhone 4 and 4s models are the same size so all cases and screen protectors will fit the same.
The screen on the iPhone 4S is made of Gorilla glass.
The iPhone 4S has the exact screen as the iPhone 4. (3-5 inch, 960 by 640 pixel "Retina Display")
try the settings
No the iphone 4s screen is slightly bigger in terms of dimensions, also the cut outs are different.
iPhone 4s is easier to use, but it depends on which Htc, I would say the iPhone 4s
You can not change the touch screen sensitivity on the iPhone.
The iPhone 5 has the serie like the iPhone 4S, but the iPhone 5 has a way bigger screen, and cheeper app prices. So i think the iPhone 5 is better
That requires jailbreaking to put widgets on your iPhone. Currently there is a tethered jailbreak for iPhone 4S But it i highly recommended that you don't jailbreak.
Clean it and get a screen protector and case
no
There is really not a big difference between the iPhone 5s and the iPhone 4s. The only thing different between the phones would be the screen size.
It is 3.5 inches from one corner of the screen to the opposite corner of the screen.