You can't.
To use an iTunes Gift Card to pay for your songs click on the Redeem link in the Quick Links box (top right) on the iTunes store home page.
You can add a video on YouTube without going through iTunes on your iPhone by uploading it directly via your PC.
Yes, but downloaded apps from Installous will not sync with iTunes.
Yes. Such as the App Store. You're going to need an iTunes account to install the apps.
If you don't know your password, you must go through iTunes. Otherwise, just enter your password.
easy just ask the person the password
no,
No, you do not need an iTunes account to reset an iPhone. You can reset an iPhone directly through its settings by going to "Settings" > "General" > "Transfer or Reset iPhone" > "Erase All Content and Settings." However, if you want to reset your iPhone using iTunes or Finder, you will need an Apple ID to back up or restore data.
You can download iTunes by going to this website: http://www.apple.com/itunes/download/
Just copy your music folder to an external hard drive if moving computers, or else a public folder if just going to another account. Add it back into iTunes then.
iTunes will not randomly delete one of your songs. You have probably accidentally deleted one of your songs without even knowing you deleted it.
It is already on iTunes.