I'm also new to the whole "Mac programming" thing. At least on anything since System 7. Coming from a strong Java background, it's requiring me to unlearn some stuff and has reinforced just how common basic OOP concepts are in other areas.
I agree that Hillegass' book ("Cocoa: Programming for OS X") is a great (and thorough) intro to Cocoa. "Cocoa Programming" is also good, but just a bit cumbersome IMHO. However, I don't see any way around getting Kochan's "Programming in Objective C" concurrently with Hillegass.
From my point of view, Cocoa provides you the keys to the GUI kingdom. Using Hillegass' examples, you'll learn to do most of what you need to learn in order to build a GUI, complete with interactions between components and with the user.
However, to actually do anything aside from GUI logic, you need Objective-C (unless you punt and use Java to fill in the gaps... as I've been guilty of doing). And Kochan's book is an excellent intro to that language - and it doesn't require familiarity with any language first (he starts at the beginning and teaches Objective-C, as opposed to assuming you're coming from C or C++ or Java or whatever background).
Before using Java, I used C++ for many years, and C before that. While I agree that Objective-C often looks like C (of course, since it's a superset), the differences are enormous in terms of how you use the language. Kochan does a great job of explaining it.
As far as AppleScript: it's great for inter-application glue. It's good (but often tedious and mystery-prone) as a simple way of interacting with apps. But it's not as good as Python, Java, Objective-C, shell scripts, or really any other approach when you're not directly trying to tell other apps to do things. It's good to know, and very, very useful in its defined area, but not a great general programming tool.