WOW!, thats some impressive traffic numbers. Makes me want to give your system a good try. with those kind of traffic numbers I should be able to get lots of traffic to sponsor with my average 10 percent ctr I am able to pull out of my ass with galleries.
One tip I can give for keeping gallery sizes down, use square cropped thumbs. A 120 x 120 thumbs looks just as big as a 120 x 160 and will probably drop a third (or more depending on how busy the image map is) off the total file size even compressed at 50 percent in PS7.
An exaple of this is
http://back-off-bitch.net/gal/ftv/mandy/index2.htm
To the average surfer or even the quick reviewer the thumbs look really large, but they aren't. A jedi mind trick someone tought me.
EDIT: ... last minute thought... Insteda of using 3 of those 250 x 250 big thumbs, use a banner, probably less bytes used, and a better CTR percentage because surfers love banners.