emacs: the best place to get emacs for Mac seems to be here http://emacsformacosx.com/ which is also the most no nonsense website design ever
Not really a Mac tip, but I stick my .emacs configuration file in a Dropbox folder, along with any emacs libraries and emacs lisp code I write. Then where-ever I install emacs I make a simple .emacs that points to the one in the Dropbox folder. This also forces me to make sure any platform specific emacs stuff is properly handled.
Clipboard: copy and paste between the terminal and other apps can be done with pbcopy and pbpaste. For example a long complicated command line you want to email to yourself, just do:
echo "long complicated bash command line you don't want to retype" | pbcopy
And then you can Command-V that into your email window. Going the other way is just as simple; Command-C the text you want and pop it into the terminal window with pbpaste.
Open: If you want open an application from the command line you can do it like this:
open -a SomeApp /Users/yourname/SomeFile.hai
You can open a folder in finder
to open that file with it's default application.
Check out the help 'man open', to see other stuff like how you pipe stdout into an application.
Finally check out this guys OpenTerminalHere script. This pops an icon in finder that lets you open a terminal window in the highlighted folder.