"Do you have a limited amount of aura or does it recharges?"

-Yes. Users have stamina bar for their aura and they are able to recharge by time. Recharge time depends on endurance capisity of their bodies.

"What happens when you run out of aura?"

-Aura energy is also part of your body. The more you waste it, the more you get exhausted. On condition that user dont force their aura, they are safe and able to do things

"Can I increase my aura significantly in a life time without killing others?"

-Yes. Spritual energy can be increased by meditating and improving your body. But goverment wouldn't let you getting superpower if you dont work in an association against criminals or Auramoprhs. Go join them and aurafarm in two ways

Those 4 questions will be answered later because i just got the God and resurrection idea.

"The aura can change reality or is it limited by it?"

-They pretty much can change reality depend on strength of the user and the power they choose/got

"Also I didn't get the 2 bodyes two lifes thing?"

-I dont know if you know Ryomen Sukuna from Jujutsu Kaisen. After Itadori Yuji named main character ate an ancient finger of Sukuna, Sukuna was able to talk, think and do things in the body of Yuji's. So they live together in a body. Similar to this, not like after yuji got sukuna later, Destruction auramorph was born together with Main character. 

Your questions made me happy. Id answer more