SD cards are smaller than USB drives. Also, what is the difference for you? Your iPad can read neither USB drives nor SD cards. Get it working, get it public, then get it pretty. That is essentially how all free/open-source projects work. Yes, they are. It is called not being an idiot and try to re-invent the wheel. But that is nothing extraordenary. Every good idea gets copied sooner or later by competitors. + mouse, keyboard, scanner and a million other devices. Pretty much every external device except the screen and headphone/speaker is connected via USB.