Hi, there's lots of room for more answers, but fyi, you can get started here
In the case of, say, singers in the Eighteenth Century, you might have a steady job singing in a church choir. This would give you lodging and food, and possibly (in the best of circumstances) a small stipend.
The real money was on the operatic circuit. But it was also very high risk: you generally only had contracts for a period of several months, and you never knew where your next paycheck was coming from. Again, contracts provided for food and lodging, and there would be some sort of monetary gain either in the form of an actual stipend or in the form of one-time gifts of some sort of monetary value. And because you were usually entering into the temporary service of a monarch or other noble patron, you also gained a degree of favor that you could use to make requests that way too. In lieu of salaries, some opera companies let the singer host a "benefit concert," the proceeds from which they could keep for themselves (this was an especially popular option in England).
If you were good/lucky, you'd also have a patron or group of patrons who supported you more long-term. Perhaps they provided you lodging and food on the off-season. In fact, they may have been involved with your musical education from the get-go. Often good students are "sponsored" through their education by a noble patron.
Only the best of the best would be able to pull off a synthesis of both worlds: they could hold permanent positions at some pristigious music-making institution, but would be on leave pretty much the entire time in foreign courts performing there. You would essentially function as a symbol of your home courts wealth and power, who "loaned you out" to perform at other places.
When you tired of singing, you could possibly transition into an administrative role, becoming an "impresario" who hired the singers and the personnel for an operatic season. This is what Farinelli, the greatest operatic star of the eighteenth century did, he retired from the stage to direct music for the Spanish court, singing privately for the king and handling the court opera. And for that service, he effectively was made into nobility.
Hopefully in the coming days I can come back with some more specific examples if you require! But for now, here are some sources for what I was saying above:
Durante, Sergio. 1998. "The Opera Singer." In Opera Production and its Resources. Edited by Lorenzo Bianconi and Giorgio Pestelli, 347-417. Chicago: University of Chicago Press.
Heartz, Daniel. 2003. Music in European Capitals: The Galant Style 1720-1780. New York: Norton.
Holmes, William C. 1993. Opera Observed: Views of a Florentine Impresario in the Early Eighteenth-Century. Chicago: University of Chicago Press.
Rosselli, John. 1988. “The Castrati as a Professional Group and a Social Phenomenon, 1550-1850.” Acta Musicologica 60: 143-79.