Is it correct to use a 9V 1A transformer to power my project?
in all places recommend not to use sources that give currents greater than 500mA when you are going to feed it by the pin VIn with 9V.


Nowhere says that.  They say you should not draw more than 500mA when you supply with 9V.

The heat generated by the 5V voltage regulator is proportional to the current multiplied by the voltage.  The more current you draw the hotter the regulator will get. The higher the input voltage, the more voltage it has to drop, and thus the hotter it gets.

So the higher the input voltage the lower the current drawn by your project can be before the regulator gets too hot.

Since you are only around 300mA that's below the recommended maximum for a 9V input.