I just want to be able to individually control volume levels of the inputed devices from a single device is the goal.
So if I am using the turntable and PC,PC and PS4, or any combo of them together its not all affected by one volume knob. I want to be able to dictate the volume levels of each individually.
If my turntable is stereo RCA out would there be any reason to convert that to TRS 1/4" or no?
I have no idea what the end purpose of all this is. I have a feeling that you are setting this up in place of a preamp, which is a very bad idea indeed.
A mixer has few and limited purposes.
A mixer is to assign and blend multiple sources for live PA, or recording or both primarily. Sometimes both at the same time.
They are also used in past production for overdubs and such. That is what mixers are for as to their core function.
In addition there are selections for monitoring via headphones and speakers. I addition there are bells and whistles these days like remembering multiple mixes and settings.
In essence mixers are ONLY useful if there is some type of audio production involved, live recorded or both.
If you are thinking you are going to drive those Genelec speakers from a cheap mixer like the one you mentioned, then you will have massive quality loss.
Does your turntable output direct from the cartridge (RIAA unequalized) or does it have a pnono preamp that sends an RIAA equalized line level signal?
You are very hard to help as you are very sparse on details and specifics, especially what the total design is for.
If there is no recording, live production or post production recording going on here then you are barking totally up the wrong tree.
If none of that is involved then you need a preamp with balanced out and the ability to handle digital and analog signals and I suspect also needs RIAA equalization for your turntable.
If you conclude that I have the feeling you are lost and adrift at sea you are correct.