Technically yes you can. Your PSN account is a Sony-wide service regardless of the device you are using it on. You can redeem a PS3 code while on the PSVita's own PSN 'app', and it will be added to your PSN account. However of course, that will not let you use the PS3 content on the PSVita.
You only need a PSN account not a new one
You use the same thing as the ps3 and psp
You can't use a PC, you either transfer certain titles from a PS3, or get them directly from the PSN.
No codes are available at sites for the free items and other items like PSN cash cards are one time use
Over 70 million people have PSN accounts that are not PS3 accounts but allow the PS3 to connect to the Playstation Network (PSN) and use it
no
You don't get them from a website, you use the PSVita's own PSN icon.
You can play with a modified connection, but if you use it to cheat you may get banned from PSN. As long as you are connected to the internet with your PS3 you will be able to play muiltiplayer games. However using a modified connection to cheat could get your account on PSN banned as well as your PS3 banned so you will not be able to play online with it ever again.
System activation is where you log onto your PSN account on a PC, and register your devices (PS3, PSP, PSVita). Only systems you have activated in this way can log into your PSN account and use your PSN data.
The PlayStation network refers to the online features of the PS3. Every time you do anything online on your PS3 you are using the PSN. You can download content, play games online, and watch movies on the PSN.
No you do not. The Playstation TV is more or less a PSVita variant, with no screen or controls. It can play a selection of PSVita games and connects to the PSVita's PSN store to purchase PSP or PS1 games, etc.
You should probably buy the PS3 or Xbox 360 versions since they don't require a code to use, only a PSN or XB Live account to download and play.