ZFR: I recall there was somewhere a formula about how experience is calculated, but can't find it. Anyone has it?
When killing a non-hero unit, the killer gets 1xp per tier of the victim. So a T1 archer is worth 1xp, while a T4 First Born is worth 4xp.
A hero (or leader) is worth 1xp per level of the victim. So a level 25 hero is worth 25xp.
Non-hero units need (tier x 2) xp to reach silver medal, and they need an additional (tier x 4) xp to reach gold medal, for a grand total of (tier x 6) xp to go from zero to gold. So a T1 archer needs 2xp to reach silver and 6xp total to reach gold medal, while a T4 Air Galley needs 8xp for silver and 24xp for gold.
[Edit: corrected the XP requirements for heroes.] Heroes need 15xp per level until they reach level 10. Reaching levels 11-20 require 20xp per level, and levels 21-30 require 25xp per level.
Unlike normal units, each hero gets 1xp per turn just for being aligned with a player (indy heroes don't get this xp). Higher AI difficulties get bonus xp for each hero.