Ive seen almost every rig have two power packs/supplies.
Can i get away with just one?
That depends on what PSU or which pair of PSUs you plan on getting, along with all of the components that your system will be composed of.
Considering the other threads you've made, you have no idea what your system is going to look like, so it's too early to answer this question. I suggest that you learn the general process of assembling a desktop PC prior to messing around with a GPU mining rig.