Core Data model - entities and inverses

I'm new to Core Data and I'm trying to implement it into my existing project. Here is my model:

Now, there's some things that don't make sense to me, likely because I haven't modelled it correctly.

CMAJournal is my top level object with an ordered set of CMAEntry objects and an ordered set of CMAUserDefine objects.

Here's my problem:

Each CMAUserDefine object has an ordered set of objects. For example, the "Baits" CMAUserDefine will have an ordered set of CMABait objects, the "Species" CMAUserDefine will have an ordered set of CMASpecies objects, etc.

Each CMAEntry object has attributes like baitUsed, fishSpecies, etc. that point to an object in the respective CMAUserDefine object. This is so if changes are made, each CMAEntry that references that object is also changed.

Now, from what I've read I should have inverses for each of my relationships. This doesn't make sense in my model. For example, I could have 5 CMAEntry objects whose baitUsed property points to the same CMABait object. Which CMAEntry does the CMABait's entry property point to if there are 5 CMAEntry objects that reference that CMABait? I don't think it should point to anything.

What I want is for all CMAUserDefine objects (i.e. all CMABait, CMASpecies, CMALocation, etc. objects) to be stored in the CMAJournal userDefines set, and have those objects be referenced in each CMAEntry.

I originally had this working great with NSArchiving, but the archive file size was MASSIVE. I mean, 18+ MB for 16 or so entries (which included about 20 images). And from what I've read, Core Data is something I should learn anyway.

So I'm wondering, is my model wrong? Did I take the wrong approach? Is there a more efficient way of using NSArchiver that will better fit my needs?

I hope that makes sense. Please let me know if I need to explain it better.

Thanks!

E: What lead me to this question is getting a bunch of "Dangling reference to an invalid object." = "" errors when trying to save.