Hey,
1. I am not sure, i died once like that and it appeared to be accident suicide (F11 that was also my steam overlay button), and my friends died once. They stepped on bear trap, healed up and after some time insta dead.
2.Using hotbar like button 1, 2, 3 etc. Keep in mind that you need space in EQ to store for example m4, if you already have something on your back. If you don't have space to put off the weapon, you can't change it, so you must drop it manualy from EQ window.
3. Spacebar is jumping now, you can jump over small fences, there is no vaulting now. If you carry too much stuff you wouldn't be able to sprint and jump. And some small barrier are automaticly crossed by you character for example you can get into train by just runing into it (in arma 2 you had to use ladder)