KDE was always my environment of choice from a design standpoint. I generally like the way it works better then any other primary interface, and the things I don't like can be easily tweaked. On a stripped down system though, XFCE is my favorite desktop environment though (it's very fast and highly functional, less "flare", for example, last I checked there is no support for different wallpapers between work-spaces, but it is quite fast, and functionally, one of the best), on a really stripped down system , I may invest in a custom configured 'box'.
For KDE, you should pretty much run your favorite application for everything. Unlike gnome you can't really "avoid the competing toolkit" as almost everything will use GTK (firefox, chrome, whatever). KDE is a bit of a strange base for a minimalist system for that reason, that and KDE4 is far from minimalist. I would personally suggest pidgin, email client, I'd probably just use thunderbird. They're just my preferences though. Whatever you do, I'd avoid Evolution as a mail client. If things are the same as the last I toyed with linux several years ago, a lot of the gnome defaults are co-dependent on other parts of gnome, meaning if you load evolution, you'd be better off using the entire gnome suite.
KDE is a very good desktop environment, you should consider XFCE though for a conservative build.