Customizing: any of my or xcal's themes (mine are all far more dated--I'm working on it, and doing well, BTW!). Stylebar, as already noted. Ecystep is a nice new one, that is simple but coded well. Static-'s themes are good, too. Like xcal's, West's might be a little complex, but Popsicle at least is put together rather well.

Beware fractal.design's stuff. Neat, but 'sghetti code galore! :) Get his themes; just don't expect them to be stable.

Documentation will be iffy, but xcal's and West's especially are well-organized. A little on the complex side, as noted, but very much learnable. Ecystep is a nice one to dive into right off, as it just makes nice use of xModules (www.ls-universe.info) without anything extra thrown in.

Also, based on your list of wants, Litestep is definitely for you. BTW, when it comes to stability, learn this:
1. Task manager's "new task" is your friend.
2. ctrl-alt-F1 brings up a menu to recycle, quit, and kill LS, as well as bring up a run prompt.

Why? Well, in tinkering, you will break things. Period. Very often, some odd little bug will have propagated through recycles and cause LS to just go nuts, and need a nasty termination and start; rarely do such bugs transfer to a stable configuration (once you stop messing with settings, it will likely work indefinitely w/ no hassles).

Stable: mostly anything but fractal's. Also watch out for themes that still use TextEdit (xTextEdit is different!), shortcut, popup (xPopup, again, is different), label (xLabel is cool), and lsbox. Some will crop up here and there, and can be problematic.