Krustyland and Springfield Heights, and a couple of others, are Expansion side-quests and won't interfere with Level Quests except when content from one is used on the main quest. Level 40-odd for Princess Penelope uses KL buildings for example.
Read and follow those guides. They show what the tasks are and in what order they will show up so you can progress and unlock further content. Your original question mentioned the Police Station, which is the first stage in the Level 17 guide. That will start when you complete the end of the Level 16 guide.