Very, very, very, very, very (etc. till it fills up a page) cool. Keep working on it.

(i'm a designer, so ignore this if you want to just take it easy ;P )

it looks good, and i'd love to see the final product. but, as dracos says, watch out for any distorted images. just one can ruin the whole thing.

only one overlap really seems to be a problem, the one near the bottom where kaylee has a chunk taken out of her forehead. i don't know if you're going to (able to?) add some filters/effects to the images to blend them and break the boxes. by no means necessary, but it could help some of the overlappiness.

i'd suggest looking at some of the image placement... you have a few where the characters are looking off the screen on the sides. you could just switch sides with those and it may give keep it all better contained.

the text could use some width, as well. it's a good font, but it's also very tight. firefly isn't very restricted/condensed. you can probably find some good free script fonts on the net. something nice and open would compliment firefly best, i think.

deffinately looking good though! :D