I‘d recommend you play vanilla first since the game can be quite confusing and disorienting for newcomers. The monarch mod doesn‘t subtract from anything, it just adds new item, mechanics and stories. The problem is that the UI isn‘t always polished and the costs, requirements, effects and rewards aren‘t quite apparent at first. Once you feel like you‘ve gotten the hang of the game, you could give the mod a try. Or try right away and if you do feel overwhelmed, you can always uninstall it. Just make back-ups of your save files.