I've gone through whats on the site and I've seen someone with a 3 gal reservoir tank. I'm planning on putting just a 1 gal tank. What is too small. Is a gal not enough? I figure one everything is full that will be about a gal and a half.
I think a gallon of fluid circulating is going to be plenty.
If this is a drag-strip car, then sure, big reservoirs are the way to go, and you can ice the hell out of them if you want to get fancy.
But for a daily driver, a big reservoir won't do as much. You're going to eventually heat up all that water anyway, and it takes just as long to cool down as it does to heat up.
Factory A2W ICs for a street vehicle, like on a GMC Syclone/Typhoon, don't have big reservoirs. The Sy/Ty IC reservoir is tiny, about a one-half litre bulge at the side of the IC, with a 13 psi pressure cap.

I think that a really big heat exchanger (mini-rad) would be more useful than a really big reservoir on a street car.