Yes, you can add other vegetables! I recommend being up to 48hr in the fridge because I never had this dish longer than 2 days, so I am sticking to what I know accorded by my own taste experience. It is true that it always tastes better when eaten right away. Yes, you can use frozen Kale, even fresh or frozen Spinach and/or Collard greens is working very well with this recipe. You can replace vegetable broth with just a water or chicken stock if you are not vegetarian. So, instead of adding 4 cups of vegetable broth you would add 4 cups of water or chicken/beef broth. Same goes for the Bouillon. You can add any that you have on hand. Also, if I am adding only water and there is no broth of any kind for my soup, I like to add 2 Bouillon cubes and adjust the taste with salt and pepper. Add smoked sausage or smoked neck bone would work wonders for this dish. (Link in this post is not paid link, I just want to show you visually what product I am referring)