There isn't a precise number when it comes to memory sizing. Wowza primarily allocates memory for its Java Heap. On a production server running a 64-bit OS this defaults to 10GB. That can be increased up to a point but with
diminishing returns. A server with your base model config of 64GB may handle your projected load. The bottleneck is likely to be network bandwidth as much as any other factor. You could see if you're eligible for our
Load Test Tool which can be very useful for ensuring that your server can handle the load successfully.