Most musicians of his kind attracted attention from various nobleman, princes, and kings. If you got in the good graces of one of these people then you would move to a palace and perform whenever desired. This allowed them to work freely and get a stipend. So most concerts were heard only by royalty and staff at first.

When he did go out and play concerts it would have been in Opera Houses. They held between 500-700 people. 50 or so would be reserved for the king and friends/guests of the king.

After that you would have all your nobleman and successful businessmen. And so on back through the theater until you got to peasants. After all the important people were in and seated then they let the normies in. They usually filled the rest of the theater. Some theaters would allow even more people than they should, safety be damned. Check out stories of the Globe Theater for how bad overcrowding for performances was.

There was no internet, tv, radio, etc. So to hear beautiful music you may never hear again, you are damn skippy people would crowd in. I would imagine there was also serfs outside who could hear, even if not clearly, the music of the orchestra resonated out and in to the cities night sky., the notes flowing over house and businesses.

So yes, it is safe to assume that every master of music filled up their little theaters they played at. It is not tike they had to fill up stadiums.