Hi!
If you aiming for a experience close to Main Campaign of DoS 2 then "Divinity Engine" is your option. There you have full power engine allowing you to create new mods, scenarios and campaign which are can be played in standalone way, i.e. without you running it. This will require you to create your own levels with level editor, writing scripts, setting triggers and etc. I should mention that script language do not require you to be full power programmer, you can master it pretty easy and you also can alter already existing things.
You also can you Divinity Engine to extend GM mode with more level templates, monsters to spawn.
So all in all what you need to do is purely based on what you want to have in the end.
Thanks! This is exactly what I had in mind. Seems I had the two confused. Creating a full standalone campaign was my goal.
