First, don't over-think your problem. It's a Mac and the solutions are usually very straight forward and sometimes PC switchers (I did about three years ago) try too hard...
Back to your problems. Forget the Apple ColorSync utility if you have a Spyder. Is your user account an administrator? If not that may be your first problem. The Spyder software is trying to write the icc profile into the system library folder and if you aren't an administrator, then no dice.
I use the Gretag Macbeth Eye One to calibrate my PowerBook, iMac, and Mac Pro. They all look nearly identical with my images so you should be able to get the same results with your Colorvision Spyder.
With regard to color space. I do all my master edits in 16 bit ProPhoto, then down convert (using edit->convert to profile) to Adobe RGB 8 bit for preparation to print. Never use "assign to profile" as that will give you unexpected results. If you really want to be fully color managed, then you need to download printer/paper profiles from your lab. You can use Photoshop's soft proofing to adjust the image so that it will look as close to your display version as possible. I say close, because most printers can't reproduce the full gamut that we see on the monitor.
You really should get a book called 'Real World Color Management
' which will give you much more detail than anyone on the forum can do.