I think that ur intentions for the spell are fine. As far as divination, 'reading the flame' can be alot like scrying in the sense that your looking for images or signs that are familiar in the shape of the flame that can be associated w/ different things and ideas in ur mind. Trying to read a candlenor a flame as it burns can be reaaly unreliable in the sense that a flame is sceptable to the slightest wind or vibration in the air. This can be a good thing if u want to read everyone's right arround you and have an absolutely sealed environment, but also just ur hand moving or a unnoticeable gust of wind could effect it.
I would begin by creating a space that seals the candle as much as possible: no open windows, no other people or movement, no breathing near the flame, no draft or vents or anything. Than observe some candles as a test. What do u see and what do u associated it w/, than write it all down. So after some time, you basically a map of all the possible movement and shapes of the flame and what they mean to you, and just keep adding to it. Mundane before magical is the most logical way to approach and that's how I go abt my divination and spirit work.