You prepared a very good plan. You can add Vienna in your list. It’s a nearby city to Budapest, which is already in your list. You would enjoy the point of attraction like Schönbrunn Palace, Prater, Vienna State Opera, St. Stephen's Cathedral and Hofburg Palace. For any tour, planning should be based on the type of places. If you are preparing list of places, define category of few cold places, few islands and some culturally richer places. This would help you to choose the correct cities according to the category. For Islands, I would suggest you to visit Solomon and plan your stay in King Solomon Hotel. Else, if you are planning for Venice, then stay in Antico Doge or Hotel Columbina.