Your Windows 8 iso file you can just save temporarily on e.g. your MacOS desktop. Bootcamp will use it when building the Windows8 installation falsdisk.
When I prepared my Mac for Bootcamp I did it in two steps. First I created a Fash disk with all the drivers etc, then I did the partitioning of the harddisk and the creation of a second flashdisk (whish is the Windows8 install disk). When using Bootcamp this second flashdrive just stays attached to your Mac while Bootcamp does its thing.
Note of caution: after Windows 8 was installed you are supposed to run the Bootcamp utiily setip (that I created on the first flashdisk). Unfortunately, by doing so my Magic Mouse started freezing on&off in Windows 8. I resolved this by reinstalling Windows 8 and installing the drivers I wanted one by one (the bluetooth ones). I got the display and sound drivers directly from Intel for my MacMini 2011 (with HD3000).