The hero value doesn't have to be equal to Freya's request. It's the value that the character you send will have to earn in valhalla in every chapter, but if you could meet her request - the better.

Also, the characters you send can "die" in valhalla if you did not give them good armor/weapon.

To build up Hero Value, level a character, and everytime they level, they gain 2 Hero Value.
Also, use Skill Points to max their traits in the Skill Menu.

And Hero Value doesn't HAVE to be exact or over, but the more, the better.

Not really,but it's for the best if it matches the description and have a high hero value.Every time a character's level increase their Value increases by a bit.Adding it manually yourself is good as well.The more perfect your character,the better the rewards you will get and your evaluation will be replenished by a large margin,which means you can take as much articfacts as you want.