I've done this sort of thing, for robotic walkers. You definitely want storage that is
easily rewritable without having to reprogram the Arduino, eg, SD card or EEPROM
chip such as 24LC256.
Then, possibly use the PC to write the sequences to the storage device, as mentioned,
or else write a little command interpreter for the Arduino, so you can insert data into
the storage devices using the Arduino terminal emulator. The latter works well, because
you can make changes and immediately test them.