Hello 
Welcome to the Forum.
In the case of stacks for physical changes it is recommended to work on no more than 4 things. So you dont get overwhelmed and see results faster.
About raising the vibration, luck, happiness etc you could listen as much as you want.
Brain fields or hormone related ones are recommended x 2 loops at at time etc. Specially at first.
Usually the audios have a listening recommendation in the description box, if it doesnt say anything it means 2 or 3.
If theres a warning, it says.
But also since you are new best its to read all here: