Hi Rok: to answer your questions:
1. Not sure what you mean here, exactly, without seeing it. Doesn't make much sense, frankly. I am assuming it is not a singer? Are you sure it is headphones and a mike?
2. You are seeing rotary-valve trumpets. The same type of valves used on my instrument, the French horn. They have a darker sound, and are more widely used in Europe than they are over here, though sometimes players here will use them, especially in rep like Brahms where they want a darker sound.
3. Yes. Always. There are a couple of exceptions which I believe we discussed long ago in this thread, if I am remembering correctly. Baroque musicians add ornaments to their parts in certain places, and the continuo part was always improvised by the keyboardist - only the bass notes and the chord symbols were provided. Another exception would be the cadenza of a concerto, which in the classical and even into the romantic era would be made up on the spot by the soloist, just like jazz improvisation, except the melodies will be based on melodies in the movement in question, though the harmonies are often changed radically. There are still some soloists who do this in performance today, though not many anymore. But for exceptions like these, however, the answer to your question is a flat yes, until well into the twentieth century, when composers started experimenting with "chance" music, etc.
To elaborate further, the same would go for film music, unless it is someone like Morricone, who wrote many of the spaghetti westerns. All he did was write the melodies and harmonies, and someone else orchestrated it.
And as I am pretty sure we have discussed long ago in this thread, even in jazz the only thing truly being improvised normally are the solos - and these are almost always based on standard tunes - very little is truly freely improvised, someone making up whatever they want. All the musicians know the chord structures used in the tunes, so even jazz is not so mysterious as it may seem. They even have things called "Fake Books" which are books that have the chord structures of all the tunes - these are particularly useful in the case of performers who are not in a regular group, thrown together for a gig, maybe none of them have even played together before. They would discuss ahead of time which tunes they will do (or even during breaks on the gig, before the next set), and reference a Fake Book if they need to. Instrumentation is generally much more flexible in jazz as well. Now in a big band, for example, everything would be written out for everyone except the solos. This is even done on something like Miles Davis Birth of the Cool, where you have a larger ensemble - much of that was written out. There were a couple of horn players on that album, by the way. A friend of mine is trying to put a group together to recreate that album, and I hope to participate if that ever happens. The problem is the guy who has the music would want to play, and he kinda sucks, so, my friend doesn't want him to play, so he won't loan us the music. Sigh.
