Is music theory essential to learning to play the piano?

You should choose music you enjoy, but just keep your guests' tastes in mind when you're putting the playlist together. You don't want to totally alienate your guests; you want...

Yes. But you need to be well acquainted because you need to have the exact note. Or, you can look up a recording and tune with that.

Yes. An E on the piano should be an E on a guitar, or it's not an E anymore. You have to make sure it's the right octave, however.

Music theory explains the fundamentals of understanding how music functions. It is like the grammar and syntax of music.

You can always write the musical and the lyrics, then ask an expert in the field of music to compose the music and play it for you. However, it would...

For sad songs, most people use minor chords, which have accidentals (sharps and flats). Beethoven's "Moonlight Sonata" is a perfect example of chords with a lot of sharps.

No, that is an original work, of which the performer/author would own the full rights.

Over time, dust and dirt can build up on your piano keys. To clean them, go over the surface of the keys gently with a wet wipe. Just be sure...

To match a piano playing a C scale, you should play the D scale, since the piano, which is an instrument tuned in C, is a whole step higher than...

The L is Real 2401 is actually a myth. There is no way to unlock Luigi in Super Mario 64. You can do it on the DS.