chuser: You also get 1 fame for defeating 4 or more units, and 1 additional fame for every very rare creature killed.
You get 1 fame for winning a battle against 4 or more units, but if you kill a strong creature, only one extra fame point is awarded regardless of the number of strong creatures.
Winning a battle against 1 sky drake and 3 phantom warriors gives 2 fame. Winning a battle against 9 sky drakes still only gives 2 fame.
chuser: Heroism raises a unit's XP to max until it reaches max XP naturally, at which point heroism will be automatically dispelled.
Also, Heroism raises a normal unit's level to Elite (120 exp equivalent) while in effect, with the spell being dispelled automatically when the unit gets there naturally. If the spell is removed before then, the unit will revert to whatever level its natural experience indicates (and it will have been gaining exp as normal while under the influence of the Heroism spell). The +1 level from Warlord and Crusade are applied after these calculations.
Heroism
won't raise a Hero to Demi-God (max level, at 1000 exp), otherwise the spell would be incredibly overpowered. I don't recall what level a Hero is given by the spell, but it is probably the level that is present when a Hero has 120 exp.