So or such?

[Genzo]

One teacher of mine taught me that: so+adjective and such + noun.
However, another one taught me similar except that in front of many/much we use so, not such. For example, it is there have never been so many people in this room, not there have never been such many people in this room.
Could you please tell me which is the right answer, so or such?

[Haihao]