You can get by with 4 pouches and mags. I'd suggest a realistic number is at least 4 pouches, and 6 mags.
I have 4 mag pouches strong side, and two weak side behind the holster, and tend to have a stripper mag in my back pocket and a stage mag in my front pocket.
DO I need 80 rounds on a stage, no. However, many match directors will set up multiple stages side by side, and run competitors hot to the next stage. It's nice to be able to do a few speed shoots and a medium course without having to charge mags.