Thus far, outside of the standard "Sith bad, we're also gonna have to deal with the Bryn'adul aren't we" sort of stuff (although I haven't gotten around to the second given the territorial distance from where the Judges have always been based), we don't have any specific rivals; if this were the old days the First Order (and really any imperial faction) would clearly be a rival group, but that's not how things are shaping up to be at the moment, and Cotan's actively trying to build some alliances to help keep the galaxy secure. Kinda like a "Luke Skywalker working with Gilad Pellaeon" deal.
Now, I'm sure at some point that'll turn into more of an in-character mostly-friendly rivalry, but the current idea he's working with is "we can't really get so hung-up on whether or not imperialism itself is inherently so terrible that we have to fight it at every step when there's bigger fish to fry; let's work with them for now, and try to turn them towards something better later on, rather than just having a massive free-for-all through the galaxy."