yes
No. Texting is a separate service that you pay for individually or in a bundled plan. Data usage is downloads, email and web browsing
I do believe it is since the unlimited data is the connectivity to the internet. Without data you have no internet. Hope that helps.
You can either buy it or if you have a code you can enter it in redeem a code.
Data usually refers to the amount of time you can spend streaming, downloading, etc. On your mobile phone. Unlimited data is no limit to how much you can do on your phone. (May not include tethering...
Not that I know of...