Why? It's usually considered to be a waste of money re-housing semi-modulars in eurorack cases - you are paying twice for both case and power!!! which is something you already paid for when you bought them
That´s true, I never wanted to be into modular, but when the QS arrived I saw that it lacks a power switch and that made me start to think about having both in a case, maybe it´s not the best idea as you say.
you will need a power supply - this one is designed to connect to a busboard so you would need one of those as well - see the description of the module - there are others designed to use flying busboards (ribbon cables with headers on them) but these can potentially introduce noise - but rack warts (power modules) take space in your case which is better used for actual modules - so cases with power inlets mounted elsewhere are preferable
do you need an output module? maybe - what are you considering sending the output to?
I barely understand the module descriptions, that´s another reason why maybe I shouldn´t do it. I thought an output could be nice to have a quick control over their output levels.