Does a dancer need to know many sequences to be a good dancer ?

No, not at all. As far as I am concerned, I never use sequences when I dance Tango in a ball. It's always a full improvisation. But let's be clear, improvisation is not mixing sequences ! It is not a matter of mixing sequence n°24, with sequence n°20 and finish with sequence n°30 ! No, the spirit of the improvisation is not to think but find movements, body positions that maybe you never experienced before. For example, I find a 'side step' and I feel like leading the woman in a backwards step, whatever her and my position. Here is the level of improvisation everybody should seek. Remember that improvisation is not mixing 'turn + gancho + sacada' with 'turn + gancho + boleo'. Good Tango dancers don't dance with sequences !

Did you notice any differences between students in Paris and in Buenos Aires ?

Here in Paris, students study Argentine Tango in a very intellectual way compared to students in Buenos Aires. It is an advantage but also an inconvenient. In Buenos Aires, students think far less and dance far more. In Paris, the intellectual approach sometimes make people forget to feel their partner, forget to embrace them and forget to feel their bodies. It is an essential difference. The intellectual approach opens access to better technics but make them lose the spirit of Tango.