Get the Apple developer tools even if you don’t plan to use them. They have helped out in a variety of cases (for example you can remap command keys in the UI of cocoa programs without compiling anything). I rarely use X, but you should download it early on, as some command line programs that manipulate graphics in memory use X windows libraries. I use Ethereal a lot in my daily work, and this is really the only pplication that I have to run under X. Xemacs would be nice under X too, but if I don’t have X11 running, then I just use emacs from the I installed Xemacs
terminal window.and Emacs from the fink project.
Fink is explained and mentioned in the Mac OS X Hints article
referenced previously.
Update: See elsewhere — there is now a simple way to build your own Carbonized Emacs which I use almost exclusively now. I might ween myself of my XEmacs habit. Stig would be proud disappointed.