tsambou I have an additional question about this: if I want to use more than one amp and my external power source is for lets say 2Amps could I use P9_5V for 1A and P9_06 for the other Amp, needed somewhere in the project?
No, they are simply connected by a trace. P9.05 and P9.06 are simply connected to the barrel jack input (which is why they will only work if that is connected), and in principle their maximum current rating would depend on the PSU's rating, and I suspect the rating is limited by the trace size on the PCB. In other words, if you want to get more than 1A, you should tap into the 5V from the PSU before they go into the barrel jack.
tsambou . I've read about software SPI
That is going to be slow on Bela (it's much faster on BelaMini!). I2c should work just fine though. Whether it is a huge endeavour or not depends on whether the chip you use has either an extremely simple API or an existing Linux library. Arduino libraries can also be adapted, though with more effort.
tsambou Is there a way I could use 9 or 12 volt for the LEDs and the chips as stated before, obviously without damaging Bela?
I think so, you should be able to power the MIC2981 with a higher-voltage power supply, but you need to connect its negative side to the same GND used by the shift register that is driving it (and in turn Bela).