Hi @pedrohead, welcome among us !
K40 is the cheapest way to go into laser cutting. The first things you want is to choose the software you will be happy with, that will command the choice for a controller upgrade.
I suggest you try first Scorch option K40 whisperer which is based on a reverse engeneering with the advantage to keep the built-in controller.
With a controller change which is now easy to do, you can go for more sofisticated softwares:
You can buy Lightburn. (Compatible all usual boards including Gerbil, but original)
Or go for Open source solutions, Visicut, Laserweb,( compatible Smoothie, C3D mini).
2 Firmwares possible, Smoothieware better for vectors cut or Grbl better for engrave run both on Smoothie board, C3D mini , easy to swap one to other by copying firmware file on SD card and reboot.
Other mods are to improve security (door switch), or efficiency (air assist). Or make your life easier by organizing the internal space to have your material at the focal distance, or reducing burn marks (honeycomb bed).