First off, I can tell you that the benefits of upgrading or changing your ROM are many depbending on what you get. Some ROMS, for instance, give you the ability to use internal GPS like you are wanting. Custom ROMS also come with a bunch of programs and other goodies built right in.
I know that it can be very overwhelming at first but you have to keep reading until you feel confident to start flashing. I would start here
http://forum.ppcgeeks.com/showthread.php?t=32382 and absorb as much as you can.
Good luck and have fun geeking out,
Yamus