(...)

If the number doesn't matter, than low it to ten, or 5.

I want something that can build up and grow with me, not some written-in-stone law that only says That I suck with one and am ok with other, maybe some people could get more than +15 with a char, wouldn't wanna try to do that?

Increasing achievements for harder-to-do ones is an ok one for me like +20 on each character. As long as the achievement points actually is "earned" and not easily obtained free after doing another achievement, it's a good idea.

The Special thing about my ideia: In order to release the +20 on someone of the kusa, you would have to had done all the +15, is it better explained this way?