Hello Aitor,
Welcome to the Forum and I really appreciate your kind words. It makes me happy to see that more traders are getting interested to learn from us.
The robustness tests are very important when generating and validating the strategies.
In order to choose which ones you want to use, you need to understand exactly how they work.
The Monte Carlo will show you if the strategy remains profitable, for example, if you change the parameters in the indicators or if the spread is floating.
Multi Market shows the results that a strategy has on the different markets. This might show you which strategy you can use for a couple of currency pairs.
Walk Forward is much more complicated, and here is a free video about how it works:
It is hard to find a strategy if you use the three of them at the same time. Best results are coming when you combine 2 of them.
Personally, my order of importance is:
1. Monte Carlo
2. Walk Forward optimization
3. Multi Market
I hope that helps and let me know if there are other questions.
Enjoy the weekend!