Can I simply throw all these ingredients together in my cast iron skillet and cook in the oven? Potential pitfalls, seasoned advice?
Yes, it's pretty reasonable to cook a beef stew in the oven.
Do note that one generally cooks chuck roast for a good long time (maybe two hours or more) to get it nice and tender, so it may be a longer cooking time than you want for the onion and potato. You could add them later if that's the case. You might also want to brown the beef in the pan before adding liquid, to get some extra flavor out of it. Finally, if you don't have an oven-safe lid for your skillet, keep an eye on it and make sure you don't boil off too much liquid in the oven; if it gets low, you can just add some water.