1: You get to choose between a bowl of rice or a piece of candy. One bowl of rice fills one heart on the hidden Hungry meter, and one piece of candy fills one heart on the hidden Happy meter.
2: Yes.
3: Briefly press and hold buttons A and C together on the main screen (not the time screen) to mute the sound. Do the same again to turn it back on.
4: There's not an official pause function. However, if you bring up the clock by pressing B, and then hold A and B to put it into Set mode, the Tamagotchi will effectively be paused until you set the correct time again and resume playing.
5: Pretty much. However, using the clock-set pause trick will extend this a bit, since time won't progress if you do this.
6: I haven't run my 20th Anniversary Tamagotchi Mini in a bit, but if memory serves, after they hatch they get through the child stage within a day or so.
7: I'm afraid I don't know all of the details on this one - sorry!
8: Yes.
9: Sort of. It shows one of two symbols that indicate if either the Hungry meter or the Happy meter have emptied, so that you know what attention it needs if you've missed a call.
10: Whilst it doesn't cover a lot of details, like growth-charts and so on, a lot of this information is in the included instructions leaflet.
11: As for when it needs feeding, it will let you know, or you can keep tabs on it yourself - these things will affect the outcome.
12: I don't know. I don't currently have batteries in mine because I haven't run it in a little while, and I haven't yet run down the one that came with it.