your swap partition size depends on size of your memory - it should be double-to-triple size. for example, if you have 256 mb of RAM, your swap should be at least 512MB, but no more tham 762mb (ther's no need)
you should do custom installation if you know what you want. i'm using mandrake and when i used custom, there were couple of levels of importance of applications (eg. xWindow = very important, mozilla = not so important, and so on) so you shouldn't be able to skip some important apps. anyway, if you're not sure about certain app, install it.
but as we're into this theme, i have a question too: is it possible to install only KDE, (without GNOME, i mean)? would that allow me to use some of the apps (GIMP,...)?