5.1 Surround sound mixing - what signals to use?

So I have a stereo sound file which I want to upmix to 5.1 surround. To do so I used Multitrack session in Adobe Audition CC. To have the entire session sound well in surround, I made a couple different versions of the file:

1. Front Left/Front Right - the volume remains the same (100%)
2. Center - Normalized to 40%
3. LFE - Here I would like to ask if when I set the track to LFE Only and at the bottom I have LFE: 0-100%. If I have it set to 50%, is this the same as having the sound Normalized to 50%?
4. Rear Left/Rear Right - Normalized to 70%

So far so good. But I have a question. Shouldn't I feed the Center/LFE channels with Mono sound instead of Stereo? Don't they output only 1 signal? Would it be a good practice to just use the stereo file or should I split it using Audition to make it mono?

Now I heard the other speakers should have stereo sound but what about the Center/LFE? What are your thoughts?