I ride clipless and platform, and I have been for a while, and I commute everyday. Here are my recommendations based on my experience:
Mountain cleats/pedals are a good choice for commuting. Road pedals will work fine, but I think unless you're really into the weight weenie Lakefront Lance thing, mountain shoes are way more practical than road shoes.
I like dual-sided pedals, but there is a price to pay in the form of more fussing/time it takes to clip in. If this isn't a big deal for you (it's not for me) the dual-sided pedals are great when you wear regular shoes cycling, as I often do. I use and recommend the Shimano PD-A530 pedals. They're lighter than the PD-M324 pedals but aren't quite as grippy. Eggbeaters are a good choice if you don't plan on generally cycling in regular shoes. You don't have to wear your cycling shoes, but Eggbeaters make terrible pedals if you're not clipped in.
Don't spend a whole lot of money on your first pair of shoes. You may end up not using them a whole lot. Remember, cleats should be torqued down *tight* on the shoes. You don't want a cleat becoming loose while you ride, that would be bad news when you go to clip out. As other posters have said, even mountain clipless shoes don't work very well for walking or general use. You'll want regular shoes after your commute.
To learn how to ride clipless, find a wall or a fence and support yourself with one hand while you practice clipping in and clipping out with each foot. Do it 50 or 100 times on each foot. You can identify any issues (is the tension too tight or too lose on the pedals? etc) in a safe manner, and you get pretty comfortable with the whole process this way. Honestly, I went straight from this to the Chicago city streets riding clipless, and I've never fallen (had a couple of close calls, but no actual falls). Clipping out both feet when you come to a stop as another poster suggested is not a bad idea.
Hope this helps. Being clipped in really does help, especially for longer rides. My commute is 2.5 miles with a lot of stop and go, so I don't usually commute clipped in, but otherwise I love it.