Best practice for implementing custom discount rules?

[hirale]

We are currently using a third-party extension for custom discount rules that utilizes the salesrule_validator_process event. However, we would like to know if there are best practices for implementing such rules.
For example, we aim to apply a 20% discount to the four cheapest products in the cart, with a maximum discount quantity of six for the entire cart.

Would adding a custom simple action be a good idea?