No wonder that I didn't found the information if they keep them secret.

I doubt ranks raise morale. There's a "push" effect to do with mass that gives ranks some value in stopping penetration (esp. useful in stalling cav charges).
I am sry I mean the "valor"? I have the German version and don't know the exact names.

Other terrain advantages - e.g. good or bad in a desert etc - probably modify attack.
You know it? I asked 3 persons:
1: +x to moral, attack and defense
2: +x to moral only
3: +x to attack only

btw. There is one number too if an unit fear for example elephants. Does it effect the moral only or does it decrease attack and defense?

I don't know about yelling but guess it's an attack boost. (Morale would make sense too, but I don't know).
One guy said me that he belives that it decreases the defense of ennemy troops too. Same with screaming/singing. Increases the own attack and maybe moral and decreases the enemy defense?