There are only 2 that I can whole-heartedly recommend:
Nate Bosch's "The Piano System" and "The Sudnow Method". Do a search for these and make up your mind. They are by far worth the money!
yes of course
Andrae Thomas is arguably the best piano player..
Yes, he i playing the piano, the guitar and the drums. Of course he has a vocal career.
Yes. Of course!
That may depends on your level and you're liking. If you're an intermediate and you like jazz, then go for jazz piano level 1, then on level 2, and so on. Or if you are still a beginner then try the elementary ones.
The best piano tuner software for Mac users is generally considered to be TuneLab Piano Tuner.
Well, Beethoven wrote for the piano orchestrally. Schubert wrote for the piano vocally. But possibly the first person to write for the piano truly pianistically was Frederick Chopin. There have been many others, of course, but Chopin was the first really great composer to understand, in your words, the "nature and potential of the piano as an expressive instrument".
One of the best digital piano guides for beginners is the "Piano for All" program, which offers comprehensive lessons and tutorials for learning to play the piano.
singing and piano of course!
The keyboard is best known as a piano because of there looks, sound etc.
One of the best sheet music guides for learning piano is the "Alfred's Basic Piano Library" series.
Bach is best know for playing the piano, or piano forte.