The Workbench wont help you much without the kickstart either.
The Amiga's OS is half in a ROM (a chip on the motherboard, called the Kickstart) and half on floppy. (The GUI is called Workbench)
You may be able to find the kickstart 2 roms on eBay but I would really recommend paying extra and going for the 3.1 Rom, its much better and doesnt require any upgrades, except 1Meg of ram.
I think Amikit and Vesalia sell the 3.1 roms for the A500, make sure to get the disks too though.
