If this spell has an area and several actors get caught up in it do all of them fill the alias and proceed to perform the package?
No, this is why I suggested you mark the alias as optional and then force the spell target into it.
If I cast this spell on one actor and then on another will the first actor keep performing the package?
No, if you want to be able to cast it and have it active on multiple NPCs at once, you'd need to create a number of reference aliases and write some code in the spell to loop through them and fill the first available one. Or, create multiple quests and loop through them, testing whether they are running.
If I stop this fake quest will the aliased actor (or actors!) keep performing the package?
No, in fact this is how you'd remove the package, by stopping the quest.
If answer to any of these questions is no then it's a step backwards from oblivion and not what I'm looking for
It may be a step backwards from Oblivion, but it's the way things need to be done in Skyrim. Don't shoot the messenger.