Call the following script “emacs” and put it in your PATH somewhere:
#!/bin/sh
/Applications/Emacs.app/Contents/MacOS/Emacs "$@"
That covers #2, #3, and #4.
For #1, put this somewhere in your .emacs file:
(x-focus-frame nil)
The emacsformacosx.com site now has a How-To page, which is where the top snippet came from. There’s more info there about running emacsclient and hooking Emacs up to git mergetool.