You'll have to read Tasso's Gerusalemme Liberata, Rita! Incidentally, Goffredo in the opera was a real person - Godfrey of Bouillon (yes, really). I saw a statue of him when I was in Brussels last year.
As for the music, lots and lots of bel canto operas have choruses - certainly most of the ones I know by Rossini, Donizetti, Bellini and early Verdi. Ballets are more unusual, certainly. Incidentally, the fast section at the end of the ballet was re-used by Rossini three years later when he replaced Alidoro's aria in La Cenerentola (which, because of shortage of time, had been written by another composer, Agolini) with one of his own.
[This message has been edited by Andrew (edited 05-02-2010).]