I am planning to compose a 4-voice polyphonic piece. I am not familiar with the classical guitar at all and do not know its limitations. However, I would like to write the piece in such a way that it would be playable on several instruments (including the piano, a SATB choir, or classical guitar(s)).
What is the number of more-or-less independent voices that can be simultaneously played on a classical guitar by reasonably skilled players? Two? Three? Four?
Are there any other instrument-specific concerns that I should be aware of? For example, would it be harder to simultaneously play two notes that have a large gap (two octaves) than two notes that are close together? Are there any issues with high notes? Wikipedia states that a classical guitar can produce sounds up to B5. (I would restrict myself to no higher than G5 anyways, because I want it to also be suitable as a SATB piece.) Are those 5th octave notes more difficult to play? Do they have a nice timbre? All in all, are they actually practical to use on a guitar? If no, then what would be a reasonable highest note to use?