Would it be possible add some feature to practice dictation using the example sentences? To test and reinforce the sound’s relationship to the character, and to practice using your input methods.
I’m looking for something that plays a randomly chosen example sentence with only characters I should know, a play again button, and it checks the characters I submit.
Welcome to the forum!
This sounds like an interesting way to build up listening practice 
Having more in-depth analysis of the sentences would be helpful, too, for other features – currently sentences are bound to the word, and we don’t have any deep analysis of what characters are in each sentence.
Would you ever want to customize what sentences are selected, or would random fully-known-character sentences be sufficient?
ever? yes, I could imagine wanting to pick sentences containing particular words and characters, sentences with recently learned words or characters, sentences sounds you have difficulty telling apart, sentences weighted by mistake rate, close integration with the spaced repetition system.
But random sentences with characters and words I have learned would be plenty for the foreseeable future.
For people who haven’t figured out an input method yet, you could provide a palette of 20-50 filled out with the correct characters, similar looking and similar sounding characters, and some completely unrelated characters.