My first topic on this forum, hope it's on the correct place...

So, I'm gonna upgrade my home studio, and I'm gonna buy the fireface ufx..

This will be my first time with a RME. I used the pro fire 2626.

I saw some videos, I read some topics, but I have some questions...
The first is: There was a master volume on the pro fire 2626 that controlled the volume of all the outputs... And, watching the videos, what I understood was that the volume knob on the ufx only control the phones and the main outputs.. The problem is that I use a subwoofer, with means I need 4 outputs.. What am I suppose to do so that the main volume knob will control at least 4 outputs (1-2 and 3-4) ?

Another question is: Do the outputs 3-4 works in stereo out of the box, or is it needed to change something on the software so that they will work in stereo ?

Another one: What do I hear on the phones outputs ? I mean, is it editable ? Because I would like to hear the software return 1-2 on my headphones, to "see" how the mix sounds like and to record other instruments for example...  And sometimes I would like to hear how the input 1 (only) for example is sounding...

And my last question is: On the videos I saw that the adat in are all in stereo (1-2 / 3-4 and so on)... What if I want 16 individual channels using the ADAT inputs, is it possible ?

Sorry for my bad english, I hope I was clear enough!!

Thanks a lot already everybody!! And I'm sorry with all the questions are noob...