I like the overall impression of the site, so it's definitely a good start. Have you considered going more down the line of albums specific to different types of photography, as at the moment, there's a pretty random jumble of images pretty much in no way linked together?
I agree about the loading times. I've got a realised 8Mb line here and it's not the fasting thing going (but it's not the slowest either), so is going to be pretty slow for lots of others. In FF, if you move your mouse too fast over the thumbnails at the bottom, it can't actually keep up and you get images lighting up a few seconds after you've moved over them, missing out ones in between. That really isn't great and I'm on a Q6600 with 2gb of RAM.
I don't see a problem with not having all of the thumbnails on the screen at once. Even if you did make the image smaller and/or the space above and below smaller, I take it you'll be adding more over the coming months anyway, so there's no point. I do agree that you shouldn't have to scroll up once you've selected a thumbnail, though. That could always be combatted with a horizontal scrolling bar of thumbnails, which could look quite nice if you could integrate it with the js you've got already.