OK, so I've got myself a convertible 2001 Mustang with the stock, non-Mach setup and I'd really like to upgrade my system but have never worked with car audio equipment before. Nor do I know much about how any of it works...

I read that the system I have is 80-watts which seems kind of low to me. Is this 80-watts RMS? Not that I really know what RMS means, I just know that that's what you look for when you buy speakers and such... Does that mean each of my speakers is only putting out 20 watts each?

I really only have enough money to upgrade one thing at a time.. and I don't know what would make the most improvement... a new head unit or new speakers. Or an amp? I'm thinking I could install the speakers myself, but the amp and the head unit might cause me difficulty.