yeah, that's it, the actual putting the card together is the easy part (i say from a hardware guys perspective), if you want a project like this, i would say you would want a completely custom made launcher, with unique abilities to make the time and effort worth it, i understand it all from a hobbyists point of view, but a lot of people would look at it and think its a cheap alternative...which wouldn't really be true unless your ordering thousands of components to get the prices right down, but its not that common to have a hardware and software guy....most of the time its one or the other with a basic knowledge in the other side of things, to pull something like this off you would probably need a small team of people, one for the software side of thing, and one for hardware design....could be quite a fun project, but that's really all it would be unless your planning to go into the flashcard business and make all the effort pay off
but yeah with the 3DS, software is everything, the hardware is little more than a DRM dongle with added storage ....unless ofc, the OP means he wants to build a sky3ds style flashcard,in which case the card is more important than gateway style cards and is actually really required