One syslog server can receive logs from any number of devices. Just set all your PIX's up the same and send the log messages to the same address. There's a free syslog server software at www/kiwisyslog.com if you want to check it out, although you get better reporting functions if you buy the release version of this.
You can use the "logging device-id hostname" command to have the PIX send it's hostname as part of the syslog message, then you can easily see what messages belong to what PIX.
To manage 5 PIX's you're probably best off with using PDM, the GUI for configuring the PIX. You can download it here:
http://www.cisco.com/cgi-bin/tablebuild.pl/pix
Here's the reference for it:
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pdm/v_30/index.htm