I've also thought about adding ads to monetize it and having paid ad-free version.
I've also thought about adding ads to monetize it and having paid ad-free version.
An example of this is http://www.amazon.com/Kanji-Pict-Graphix-Japanese-Mnemonics/... , which also offers the pocket size http://www.amazon.com/Kana-Pict-Graphix-Mnemonics-Japanese/d... . I've owned Kanji Pict-o-Graphix for almost a decade, but I also bought the cheaper, pocket size Kana Pict-o-Graphix for my brother-in-law (who hadn't studied Japanese before) before our trip to Japan.
I think you wouldn't want to offer less that one full alphabet, so people can get a good idea of what it will be like to learn using your app. If it's just a few characters that they can practice with, then they won't spend enough time with your app to make them feel like they should purchase it over trying another one out.