You can purchase OS X Snow Leopard from the Apple store (similar to the ISO approach)
Take a look at this article on how to create a bootable USB OS: http://osxdaily.com/2014/10/16/make-os-x-yosemite-boot-install-drive/
Yes, you can clone your Mac hard drive and make it bootable.
The cloning software will clone everything for you.
Carbon Copy Cloner is a great software tool. Click here: https://bombich.com/
To answer your second question:
If you have an Intel Mac you can boot from either an Intel cloned drive or a PPC cloned drive.If you have a PPC Mac you will not be able to boot from an Intel Mac clone.
Correct -- they all have Intel so it will work for all of them. To answer your question about the hardware, there should be no need to install any drivers.
The OS comes preloaded with drivers
Yes, the 2008 runs on Intel.