lol The first Final Fantasy is not very long, because it was originally made for the NES. I highly recommend that you play VII. It has a vast storyline, and has very memorable characters.
Don't feel overwhelmed, if you are. I have not had time to play Final Fantasy games. I do recommend that once you start another one, stick with that one until you beat it, and then move on to a different one. Each Final Fantasy has its own feel, and battle system.
Just to let you know, all of the Final Fantasy games from IX and below do not have the greatest graphics, but it is the gameplay, storyline and characters that matter the most.
I hope you enjoy them all. XD