Netflow implementation strategy

Hi I recently configured netflow v9 on my routers. I collect them with pmacct and write the data to influxdb and use grafana for showing the collected data.

I create my template like this:

Match ipv4 dest address Match ipv4 src addresa Match udp src port Match tcp src port Match udp dest port Match tcp dest port Collect counter bytes

Now that i have configure netflow i have lots of questions!

What fields should i collect in my template to have enough information about my network?(like who uses the network traffic most?- how much of WAN utilization is unneccessary traffic?)

Where should i locate my exporter?

Number of exporters?(in network with more than 400 users)

Which interfaces should be monitored?in which direction?

Any answers will be appreciated