Yes, essentially that is correct.
Ocassionally I'll do a quick and dirty mastering at the end of a mix... (naughty me!)
But yes, once you've finished mixing bounce your project to aiff/wave 24 bit with no dithering and the same sample rate of the project. Try to give yourself at least 3 to 6dB of headroom on the Output channel...
It's then much easier to work on a single audio file when mastering in a new project.
I'd recommend Steve H's Logic 401 : Logic's Mastering Toolbox:
Essential viewing IMHO.