Welcome to SLKWorld sonic02stang!!
You don't need to do an ecu upgrade with the pulley kit, but I'm sure it would add to the fun factor. Someone here could elaborate more on the advantages. At some point I'll do the pulley kit myself, too.
You might also consider the MAF (Mass Air Flow) kit. It relocates the sensor closer to the throttlebody so as to help overcome the delayed acceleration response near 2000 rpms. Here's a thread explaining it further and a good source for the kit.
http://www.benzworld.org/forums/r170...t-98-99-a.html
You might also consider a module for the top.
http://www.simpleroof.de/
I have the EasyRoof and I love it!!
Enjoy your car and as Doug said...POST PICS!!