Jakov, more portraits than musicians-at-work indeed: the street was crowded and getting the two simultaneously was difficult (I only had a 300 and a 50mm lens; 28 would have been fine). Also, the excellent guitarist most of the time minded his very active finger business.
Armando, indeed #1 is one of the few shots with eyes locked - and very different glances.
Elsa, I confess that the 300/4 PF is very helpful for getting nice portraits, provided you can stand away. Distant background and reduced clarity for the soft one under #2 (due to his rather dark skin and shadows when eyeing down on his guitar, most other shots were making him look "hard"). #3 is exactly the opposite - close background that I could not throw OOF, so I took the other way round and pushed clarity and contrast, especially on her face, not elsewhere in order not to push forward useless details.
Frank, no idea. They did not sell CDs, nor did they distribute ads or biz cards. I guess you could meet them rue de Béthune.