Do you have a favorite character, town, scene, enemy, magic attack, or limit break? Maybe not even your favorite, but something that has meaning to you, like a boss that you just couldn't beat when you were younger, or a town or building that has some special memory attached to it. Since general form and colour are really important in abstract, maybe something colourful like the gold saucer fireworks scene, or an Ultima attack, or Cloud's Omnislash? I'm just shooting ideas of what I'd try and do lol.
Ahh, I lost my train of thought, will edit this *if* I can think what I was talking about XD. Art class was a long time ago now =_=