I am always a proponent of starting with the end goal and then working backward. What are the end results you are aiming to achieve (or aiming to allow your audience to achieve)? Is marginal precision more important than the speed impact? The optimal database design will depend on that (i.e., on what you are optimizing for...).
It would also be very helpful, imho, to indicate keys and indexes, perhaps by modifying your schema diagram, or simply (and maybe better), just dump the actual SQL schema definition (i.e. the output from sqlite3's ".schema" command)
It would also be very helpful, imho, to indicate keys and indexes, perhaps by modifying your schema diagram, or simply (and maybe better), just dump the actual SQL schema definition (i.e. the output from sqlite3's ".schema" command)