I have some doubts about QlikSense, I'm still a bit noob in this world, so I would like to help you with these questions.
1) Do we have any best pratices document for QlikView / QlikSense S.O (Windows)?I did not find anything like it;
2) My cluster has 250Gb and 20 CPU each machine (We have four), every time the system consumes only about 30% of this (about 80GB), however the OS is paging 50GBs which for me personally is absurd, this it's normal? So I asked for the S.O document to validate.
3) Do we have any best hardware practices for QlikView and QlikSense?
4) My biggest problem today is that all the data seems to load fast the first time, but when I apply filters this gets very slow and it takes several minutes, slow filters, does anyone have any ideas?
There are a lot of best practice-stuff available within the community and the most important part is to create well-built datamodels because everyting based on them and serious mistakes there could often not be compensated with smart UI's and/or big hardware. Therefore I suggest to start here: Get-started-with-developing-qlik-datamodels.
In regard to your hardware-question and possible issues by various settings take a look here: qlik-scalability.