Wait, why not requirements for the first rank?
Im thinking in terms of the first rank being a new recruit.
They might not care about your abilities and just expect you to train them.
Some guilds could be different.
In Oblivion, the mages guild's associate rank was really like, "you like magic, but your not a mage yet"
Like Erthor, who should have been an associate. He wasn't really much of a mage, he dabbled in it, but had no real skill.
So for the associate rank, at least here, there isn't a need for requirements because they expect you to train into your position, and it would make sense in this instance
Then again, the dark brotherhood probably cared about your abilities even at a low rank. So I guess it would be guild dependant.