1)Vegetables can be changed to liking. Some that I often use are bell pepper, carrots, kidney beans (for protein boost), asparagus, artichoke, etc. However, Tomatoes should always be used.2.) If the paella starts to burn or the rice is not cooked through after 20 minutes, you most likely did not use enough broth. If it comes out too soggy, you probably used to much. 3) Careful adding salt. If you are worried it might get too salty. Water down the broth before adding it.