Local codes will dictate whether you are required to install one or not. A disconnect switch is, however, a great safety feature to include even if you not required by code to have one.
Q: Can I use a key lock system to interlock the connection box and my breaker on the generator system?
Yes, but there must be a single source of supply for the locks so they are compatible.
Yes, but load bank and temporary generator have different twist lock connectors so a transfer system or switch system would need to be part of the design.
