Last year was the first time I connected through AUH and found it extremely easy. 2:50 minutes is plenty of time to connect.

I cannot recall if you have to go through security again, but if you do, it should be relatively easy. I did because I connected to a flight to the US and security was right at the gate, but not sure if all flights do that. There is security just to enter the terminal IIRC.

Distance to gate is quite walkable. In fact if you want to go to Terminal 1 you can walk that quite easily, but you will have to go through security to get back to Terminal 3 IIRC.