#1: To get a basic CS:S server up and running on Windows, I'd recommend doing something very similar to what I wrote about CS 1.6 here: viewtopic.php?f=46&t=4021
. CS:S is just in a different folder (sourcebase). The menus method is the fastest way to get going.
#2: You shouldn't need to install any of the roles for straight game server hosting. If you want to do IIS-based webhosting on the same machine, the IIS-related role might be useful to you.
#3: The server should come with basically everything you need to get started, if you are just running a server for yourself or your clan. If you are looking to sell servers to others, I'd recommend that you install a FTP daemon such as FileZilla to give your users less than full administrator access, and you might also consider installing a full-blown control panel like TCAdmin.
#4: I talk more about basic security here: viewtopic.php?f=44&t=4025
. Mostly, it boils down to shutting down the "Server" service and not using the server for anything but your game servers.