Hi Oliver.

A 5 strings is actually a Violin with C string. But the sound is really depend, normaly the E string will not sound really bright like normal violin, it will sound abit darker ( like Germany violin ). 

The main Idea for 5 strings is to play baroque music, or other traditional music ( which you can improvise both bass line or melody line ). Like in Norway you can see some profesiors use 5 string to play Bach, and improvise Bach around all the Key 🙂

About orchestra, There's no rule to fobidden 5 strings in Orchestra, but people normally find themselve become too different than the other ( orchestra should be an idea group with everybody the same ), so 5 strings is not recommend in orchestra for that reason.

Have a nice day Oliver 😀