Question: I am looking for a good microphone to record a piano. This is whole new field to me. I looked in the Internet and I found a few places stating about what I shouldn't buy, like, dynamic range microphones.

What characteristics should I look for when picking a microphone (or set) to record a piano?

Would recording directly from a digital piano give me a better quality (although with less dynamics possibilities)?

Answer: 
Rather sadly, you'll probably get better results from a good digital piano than from microphones on a real one. Unless it's a really nice piano in a really good-sounding room. You'll have noticed I didn't say "and really good microphones". They matter, but not as much as you might imagine.

If you're after "classical" solo piano sound, record stereo. But remember, an audience normally sees a piano on a concert stage sideways on, from quite a distance. In this case "stereo" will be about placing the instrument in a reverberant space, not about "low notes to the left, high notes to the right". This is a mistake made by the sound sets of many digital pianos.

But you will probably not get the results you want from hiring a concert hall and putting a stereo pair in the best seat! You'll fake the stereo ambience from some combination of close and medium-distance micing, and artificial reverb.

I'll get shot down for this, but I've made some very pleasing acoustic piano recordings with a pair of Shure SM57 dynamic mics. And you may be in a position to try this, with no immediate expense! Do you live in a world of modern performing musicians? Grab a couple of SM58 mics, take the balls off - they become essentially SM57s. (Don't drop them though!).

If you have no gear at all, there's another approach. Buy a Zoom H4n or similar, put it on a stand in front of the piano. You'll be surprised how close the result is to a recording made through much more expensive gear. And even if you progress to more sophticated equipment, a good portable recorder is always useful.
Unless you really want to become a sound guy, just get a Zoom device.

They're about the only simple way to record an acoustic piano.

Like <http://www.sweetwater.com/c733--Zoom--Recorders>

Seriously, there is just too much physics to figure out.