A daily bath can use 80-100 litres! I bet that 2-seat jacuzzi bath i looked at yesterday in Global House used more! so maybe if going with the central boiler it would need to be uprated. Like I said, the boiler option for the master 'wing', office and maybe the kitchen requirements too (there is possibility for such sharing, as the kitchen is below the master wing) and individual water heaters for the other rooms
The boiler might not be the option for the whole house as it would be long pipe runs to feed the other 2 bedrooms in the other 'wing' (building 3)