This varies widely from one orchestra to another and also depends on the particular piece being played.
4 usually.
Yes, it is. Lots of classical music is played by a symphony orchestra. There are thousands upon thousands of classical orchestral works - too many to list here.
classical
Specifically using the name "Classical Symphony"? Serge Prokofiev, who wrote it as a tribute to the classical era composers of the past.
Early classical to today!
The baroque concerto influenced the development of the classical symphony by introducing the idea of contrasting solo and orchestral sections, which later evolved into the classical symphonic form.
The 80's
Yes and no, a symphony does have an alto sax sometimes but it is not required for it to have one. It really depends if the symphony is classical, blues, or jazz. Jazz and blues should always have an alto sax. Classical doesn't really need an alto sax, but it does make classical sound better.
5000
A full symphony orchestra could easily have 80 people.
Romantic. The answer given doesn't even begin to scratch the surface of the Symphony's complexity. It is both Classical and Romantic. It maintains some of the Classical disciplines that dictate how one may compose a symphony, but it also abandons some of these disciplines and pushes the boundaries greatly on the Classical Style and intent so that Beethoven is better able to express his innermost feelings.
As a general rule, a classical symphony has four movements and a classical concerto has three. The nature of their respective first movements and finales is likely to be similar in each case. Each genre will also usually have a slower, more lyrical movement. What a symphony will also have, and a concerto will lack, is a movement cast as a minuet and trio or scherzo and trio.