Why do I need a starter kit not just the CellMons or WatchMon

We sell the starter kits to help customers procure the right components and avoid missing parts . The raw components are also available for those that are generally repeat customers.
Whilst the cell monitors (i.e. LongMon) will work without a supervisor "WatchMon", the key function of the supervisor is to monitor the cells. When the Watchmon detects that the cells are outside their limits it will attempt to notify the connected remote system with a warning to alter operation. Ideally warnings brings the battery back into its operating limits. If the condition escalates the supervisor will trigger a critical event and attempt to interrupt the battery with a contactor / circuit breaker. 
All the cell monitors need to be activated/commissioned using the supervisor to configure their operating parameters. Part of the commissioning procedures also provide a method to verify that the cell monitor has been installed properly and should be completed prior to unsupervised use.