How would one create a new faction?

[grimsurgent]

I'm not sure if this is possible, but is there a way where I can create my own custom faction, where I control what they wear and what weapons they use?

[Jimyoda]

Yes, absolutely. You can mod in your own faction. Though I can't help. To learn about modding start at http://rimworldwiki.com/wiki/Modding_Tutorials
If you haven't already, search in Mods for relevant threads and you can ask for help in "Mods > Help".