Not often, but when I do, I often play preludes by Bach and Chopin.
As I said before, Bach and Chopin Preludes.
Nope, I've got perfect pitch so no need for ear training.
Nope, I'm not a singer and even if I were, I don't know of anything made for Alto singers in particular. Back when I was 10 years old, I could sing tenor, alto, and soprano. But then as I went into adolescence, the tenor range got cut off immediately and the soprano range got restricted. It started with an upper boundary of G6, and over the years that upper boundary went down to F# and then eventually C. Now, I can articulate higher notes than that C with my voice, but it requires me to reach the high C first, I can't do it unprepared. And even if I could, my Soprano is terribly squeaky, so I tend to go down an octave by instinct instead of staying up there. And yet, most vocal works and exercises I have seen have been for Soprano, Tenor, and Bass. Sometimes I see the Tenor exercises and works with an Alto option, but nothing that I have seen is primarily for Alto, which is my natural range.
The transitioning between 2 themes, I do that all the time in my compositions, so no need to practice that as an exercise. And 4 part writing I rarely ever do. I've written chorales in several of my pieces(like for example the Bb major section of my Summer Evening piece), but they often end up in 6 or 7 parts, not 4.
I treat every arrangement I do for orchestra as an exercise so considering that I have arranged Eine Kleine Nachtmusik, Prelude in G minor by Rachmaninoff, and the Pathetique Sonata for orchestra, yes.
I did that in my early years as a pianist, but now, I just transpose on the spot, no exercises needed. I can even do major to minor on the spot(example, taking an E major melody and transposing it down to C minor)
Yes, especially the orchestration exercises.