Beginner gardener – seed sowing – how many seeds per cell in a seedling tray? And a small container?

It must be so obvious that sites don't specify this but I have no clue! And feel so silly

I sowed:
– pack of 120 seeds of bunching onion (spring onion) in a 10cm container (IN THE PICTURE)
– 10 radish seeds in a 10cm pot
– a couple radish seeds (4-5) in each cell within a seedling tray. Is that too many? Are you meant to do one seed per cell?

Is this all wrong?