So I am under the impression that if I were to install TAILS to a flashdrive, I would be able to run it from any computer, since it runs on its own operating system. This may be overly careful, but being in an area where things like TOR probably stand out to the ISP, I am a bit paranoid of making purchases. I have already installed TOR on a different flashdrive to browse The Marketplace. But would it be safe and anonymous if I were to run tails on a public computer at say, the library? Could I potentially place an order from a public computer to my home address, and be fine? If I run it from a public computer, would there be any need to run I2P? Would TOR be safe if it isn't even on my IP or computer, or does TOR's risk come from something else?
Firstly as an end user, you are very unlikely to come under suscpicion unless you are buying for resale in your immediate area. Secondly; I'm assuming if there is a library nearby, that there is likely a McDonald's or other "Free Wi-Fi" establishment. Use this over your library connection. There are likely more users and no login required.
I2P is not neccessary and has a few holes IMO. It is resonably useful for email and chat. Just boot Tails and buy away.
Consider running a bridge or node from your home (limiting the bandwidth of course), so that many users' traffic runs through your ISP. Add to the network you are using and it will add to your camoflauge. Just don't run an exit node unless you want a knock on the door for someone file sharing some nefarious stuff via your node.