Reply to Audio interface general questions

i am looking for a usb audio interface for my set up but i am noob and confused about what i really need, i dont know how exactly i could use some inputs/outputs of the soundcard
balanced/unbalanced/trs/xlr/line/phono/Headache

i have Maschine and a midi keyboard,i will not use other instruments such as guitar,i want something with low latency,midi in/out,balanced outputs for monitors and inputs through which i could connect an external cd player or dj controller(?)

i dont know what i could connect to the balanced trs inputs that many interfaces have and if i need them

lets say that i have a dj controller with traktor and built-in soundcard,is there any way to connect the controller to the usb soundcard and record/get a loop in my daw?

mic inputs: you can use a mic but most have also a choice of Line or Instrument,so what else could i connect here?for instruments i know that you can connect a guitar for example but in "line mode"?could you connect a cd player to get sound?the sound quality would be ok?

i am looking for the following:
-Focusrite scarlett 8i6: many complaints about drivers but seem to be solved with latest updates(?)
-Komplete audio 6: cant monitor 3/4 output (-)
-Steinberg UR22: only mic/midi inputs (-)
-Roland quad capture: cant control volume of headphones and monitors seperately (-)

also most interfaces are usb powered,is it stable or it is better to choose an interface with external power?

thanks