It is unbelievable that Hari Seldon would burn alive the warden of Terminus, and then would justify it that it was done to make people fear Hari Seldon. This act destroys the entire character psychology of Hari Seldon and he is no better than cruel Empire or any villain.
Hari Seldon was a mathematician, he was no way any applied scientist nor a technologist so he could not have made the vault and whatever is shown inside the vault.