voice leading for orchestra?

Hello everyone, I'm new to the forum and wanted to ask people that are way more intelligent and practiced than I am some rather stupid and probably very basic questions.

I have a strong love for music. Even so, I chose not to pursue a college degree but decided to study independently instead. I have read (not memorized) some various books and feel like I have a basic understanding of theory, counterpoint, and orchestration.

So, here is the precursor to my rather stupid question(s).

My theory text spends a lot of time having you write in four-part harmony trying to avoid "forbidden parallels" and the like, all the while informing you that these rules are for common-practice music and that newer musical styles do not take them quite so seriously (if they don't disregard them completely). But, as I made the transition from my theory text to my orchestration text, there arose a question for which (as far as I was aware) neither text seems to provide an answer (Possibly because I misunderstood some obvious implication, was generally not paying enough attention and therefor missed it, or I am just plain not smart enough to have deduced the rather obvious answer...).

And now the stupid question(s).

A full orchestral tutti has many more than the basic "four voices" interacting and moving independently all at the same time (goodness knows that even a solo pianist can, and often does, muster more than just four voices!). I don't understand how I'm supposed to avoid "forbidden parallels" and maintain independence of the voices (while writing in a common-practice style) when such a task seems practically impossible!

Are these rules mainly for the choral SATB style and otherwise not taken quite so seriously? I've heard multiple times that,"If the individual sections of the orchestra are written well, then the whole orchestra will sound good." Does this mean that I am supposed to make sure that the individual sections have good voice leading within themselves and the contrasting timbres of the opposing sections will cause them to maintain their independence or is the saying total poopiness and should be disregarded completely? And if I'm interpreting the saying correctly, then what about when many of the string sections are playing divisi? With the homogeneous sound that the string sections possess as a whole, how am I supposed to maintain independence in the voices? Am I just not good enough at composing to handle these situations? Is it just that avoiding "forbidden parallels" is far more important when you have multiple melodies playing in contrast to each other (counterpoint) and doesn't matter that much for the chordal accompaniment that the rest of the orchestra provides as a background in a tutti section? Why do I want this "independence of the voices" when that part of the orchestra is just providing a chordal/harmonic background to the more important melody/melodies that are playing at the same time? Maybe the practice of four-part writing throughout the text is just a preparation for counterpoint and isn't really so important in homophonic music? (If so, it would've been nice if they would let me know these things.) How would the great composers of the past have done it (taking into account the differences in style and compositional anal-retentiveness of the period in which they were composing)?

Any help that you can give me would be GREATLY appreciated!

First of all, if you care about the traditional rules of voice-leading then yes, they apply to an orchestra quite as much as to any other ensemble. However: It is important to note that these rules are specifically meant for two or more distinct and "independent" voices and not just instrumental parts. What does this mean? This means that different instruments may very well play the same voice in unison, in octaves and sometimes even in fifths, without breaking the rules mentioned above. When a flute doubles a string melody one octave above, this is not a case of parallel octaves, since both are playing within the same "voice". They merely give this voice a different colour by playing together like that.

When however the flute plays a quite different voice than the strings and suddenly, without interruption plays a few consecutive octaves with the strings before "going its own way again", you have parallel octaves, and should try to avoid it, according to traditional rules.

So the main idea is to get a clear idea of what -voices- you currently have in your piece and which instruments are playing them.

And while voice leading technically also may apply to chordal structures, it is often somewhat less noticeable there and in certain cases having some parallel octaves/fifths in decidedly chordal accompaniments is quite acceptable, but it's hard to give a definite answer on that, since it depends on many factors (also on how hidden those parallels are, e.g. whether they are exposed as bass and top voices or not, etc.).

It is also true that many composers of that time -did- occasionally write parallel fifths and octaves in situations in which they normally would not be acceptable. The main question here is how -consciously- you are doing it. If it's a conscious choice of colour, there's nothing wrong with it. If it just "happens" to you, while wanting to stay within the general rules of common practice tonality, it's a different thing however.

A consciously used parallel fifth in a "classical" piece of music can be the most wonderful thing ever.

Thank you so much, a very good answer. It helps me out a lot!