Hey mate
You already have the ability to create an unlimited number of faders within the software.
The master faders on the live page should be used for just that, "Master" Faders. To create a regular fader, create a 2-step scene.
Let's say you want to turn a fixture's intensity up and down with the fader. Go into steps. Create two steps. On the first step, have the intensity on 0, on the second step, have the intensity on Max. Make sure you set the fade value to "snap". Save this steps file, then go into live mode and add it as a button. Right click the button and set it to "fader slider". And hey presto you have a fader! You can then map this to your MIDI controller by right clicking and selecting "button trigger"
Watch this video from about 5 minutes
https://youtu.be/1bU9tlY6_1EHe explains it pretty well. He creates a 2 step scene around the 7 minute mark