How to set how much exp a hero get?

What i mean is, When we put our mouse on a hero lvl bar there, we can see numbers for example: 2000/3000

Ok, so can i set the amount of exp into numbers for each unit, for example: A hero is lvl 3, and his exp is 1000/3000, X creep has 200 exp, Y creep has 500 exp. When the hero killed X creep his exp became 1200/3000.

Can we set that? Other than using percentage that a hero can get? Or can we set that in Unit editor?

And what is "stats - priority"
All units have diff. Does it means tt the higher priority a unit has the more exp it will give to a hero?

Another sub question tt i just tot of,
How to make the tree not to face up, I dunno how to explain this, but just see the below pic:
http://www.elilz.com/pics/119.gif

I believe you can adjust this in Gameplay Constants under the Advanced menu bar in the World Editor.

Priority is what units ai consider to attack first. If something has a priority of 16, then everything will aim for that thing first; likewise 1 would be aimed at last. A units level is what determines how much exp they give.

Im assuming you want the trees to be angled when on a hill. I forget what its called exactly, but I think that can be edited with angle something under Art for a unit in the Object Editor.