Issues on Arduino, LiPO battery and two mottors setup
If the load on the two motors rise, could the Arduino be damaged by this current increase?


No, the motor current doesn't pass through the Arduino. It is completely separate.


  Is the voltage too high for the Arduino handle?


Borderline. The regulator (a lowly 7805) may well get very hot at that voltage (depending on the Arduino's current draw) and go into thermal shutdown.


  Is there any more issues that this setup can have?


Maybe add a small buck regulator to the 5V pin instead of using the on-board linear regulator. That will not overheat and will be far more efficient making your batteries last longer. Often marketed as "UBEC" (Universal Battery Elimination Circuit) and used throughout the model vehicle industry these are very easy to get hold of and are ideal for powering things like Arduinos from batteries like this.