EZServe is the Controller. The Unit number must be unique for each Scene where EZServe is the Controller. You pick the Unit number. Start with 2 and increment by 1 for each new Scene where EZServe is the Controller, 2,3,4,5, etc. You could start with 10 or 20. Do not use Unit 0 or 1. EZServe used Unit 1 for its own use (which I think it no longer does) in the past so to be safe start with something above 1. Maximum Unit number is 253. Unit number 254 and 255 are valid but Insteon has some special uses for either 254 or 255 for All On function so avoid those two numbers.
LD1 is Bright Level
LD2 is Ramp Rate – not all Insteon devices support a Ramp Rate. .1 works for those devices
LD3 is Output unit number – 0 for single output devices, SwitchLincs, ToggleLincs, ICON switches, etc
Each responder device linked to the scene can have unique values for LD1/2/3
EDIT: to turn the Scene ON, specify FF in the Effect Value, to turn the Scene OFF, specify 00 in the Effect Value.