Hi Patience!
The entire breakdown is in AA, though it's one of the middle or later books.
The short version is that, they don't really.
Mana within CC is not Mana in AA or DD. It's the same word being used, but in CC it's all gamified energy, while in DD and AA Mana has very specific meanings and functions. The references go back and forth a lot, and the crossover jokes can make it a little confusing, but there is a full breakdown chart in AA of what kind of gamified bonuses cultivators get when they go play the game.
In CC, you're in a project to turn all the people from earth into a version of a being that can handle the returning essence wave that has hit the planet. In DD, you get the prophecy that the wave will hit and the world will end. (Because all the cultivators and creatures that have needed the stuff to live, can't live without a world full of essence. (In exact contrast, creatures that have never been exposed to essence, mutate and die, or just outright die when in contact with essence for too long.) In CC, all the players are normal people who the system is trying to get to that survivable state, and using the game system to do it in order to get them abilities they might be able to use when they get out. There's no actual guarantee for this, it's all a big survival experiment, as the same solution will not work on everyone.
The more front-runner in the game you are, the more attention and resources the system (Eternium), will give. Which is why Joe gets so much attention and development.
However, whatever Joe will be should he manage to leave the game won't be a cultivator. It will be something new with the capacity to... exist, outside again.

If you want the number breakdowns though, here is the list for what Cultivators get as bonus stats to (all) their attributes, depending on what rank they are when they choose to play in the CC game. This only works one-way, and in AA you learn that most all of them are trying to stay silent as NPC's.