Wedding themes that are not a natural part of the location (garden theme) or the couple's ethnicity (Indian, Scottish, etc.) have gone by the wayside. To add a contrived theme is so Hollywood (which is where the trend originated.
A theme wedding would be nice, because pure theme weddings are not so common. Usually it's a beach wedding, garden wedding, Mexican wedding, Indian wedding etc etc. But if you are daring to do something different like a titanic themed wedding, or a space themed wedding people will remember your wedding even after many years. They may forget your face but they will surely remember your wedding. The best way to follow upon it is by contacting an event planner. They will have different ideas will help you in conducting your theme wedding.