I would like to develop my code in C++ WHAT IS THE BEST TOOL FOR PROFESSIONAL STM32 DEVELOPMENT?
For educational purpose I prefer a free IDE.
That's fine. I am prepared to negotiate the licence such that you can use your desired IDE.
If you can't afford my tools, you could do a lot worse than consider the Keil offering. I'm sure you have already noticed they provide a FREE development environment for the STM32L0 and STM32F0.