I have been fishing a lot and I noticed I gained experience, and I managed to get one level up, but after thinking a bit about it I have some questions, anyone could help me sharing info?

1) You gain exp by performing ANY action (fishing, foraging, JUMPING, scavenging, any crafting,etc..)? Do you have to be successful in performing the action before gaining exp or while failing you also get it?

2) Every action that gives exp, gives the same? For example, fishing 1 fish gives the same exp as scavenging 1 item or craft?

3) Hitting players give exp too? Or killing them? I mean, combat actions give exp too?

4) Do you get less and less exp over time? For example, If I level 5 levels by fishing, then performing fishing again will still give me the same exp (or performing any other action, like scavenging)?

thanks!