I would like to start programming on Mac. I have some questions:
I don't really like Objective-C and I somewhat know C, I read that Objective-C is a "dialect" of C - is it possible to program in C and use all the libraries and frameworks provided by Mac OS (this is Cocoa, right?)?
is it possible to draw GUI in XCode's GUI Builder and then fill the logic in plain C?
if I want to use, say, Scintilla - how do I "load" its text editing component into a window in GUI builder? And how do I access its text buffers? And events?
Just learn Objective-C. It isn't that hard; much, much, simpler than, say, C++. The object model is extremely similar to Java or SmallTalk.
The entire Cocoa stack of APIs are all in Objective-C, the documentation is all in Objective-C, many of the design patterns (KVO, KVC, delegation) are inherently Objective-C isms and all of the examples are Objective-C.
You are going to have to have a working knowledge of Objective-C to effectively program the system anyway. Any attempts to avoid Objective-C is just going to make your job harder, yield less maintainable code, and vastly reduce the # of folks in the community who can help.