Jodiann I am not sure I completely understand the question. Tonfotos works perfectly with any folder structure, and 20 000 by far not the largest volume it can successfully deal with. Tonfotos does not copy your photos, it deals with it right where they are, it only creates database of thumbnails and other data to simplify your browsing experience. It can let you navigate your photos by folder, by date, by people, by tags, and so on.
I would suggest you install free version first and see it for yourself. Free version has no time limitations and you can play with it as long as you can. It only limits amount of people you can add to your library. Once you decide that Tonfotos is what you want - you can buy your serial number and activate it any time. No strings attached.