Now try more coins or coins on both hands at the same time. I can catch six coins (3 with each hand at once) and four with one hand. It seems possible to do five coins.

To make the trick more impressive (difficult), limit the amount of upwards distance to the throw, and the amount of distance below the initial throw point for the last catch. As an example, with three coins I throw them up about 10cm, and the last catch is about 10cm below the initial throw point.

Flatwise:
A more difficult version is to catch each coin flatwise. The first coin is caught between the thumb and the index finger, the second is caught between the back of the index finger and the middle finger, and so on. The trick can be made easier by reducing the amount of spin on the coins when they are thrown. I can do this with 1 coin consistently, two coins occasionaly and once (probably never again) with three coins.

Edgewise:
If the flatwise version wasn't hard enough try to make each catch edgewise between pairs of fingers. This is extremely hard and I can do it with 1 coin about 1 time in 50.