Do i just need 1 of the 8 to install?
You can install using the network:
Debian may have changed the dependencies in the 1-8 series, but the original intent was that the first CD would be complete enough to install a minimal/usable system. For anything interesting, you would need CDs 2 and 3.
Only the first CD is necessary for a basic Debian installation, but the others may be necessary depending on which additional packages you want to add during the installation. Also, you’re better off downloading the DVD ISO instead since they’re 4.4GB each as opposed to all the individual CD ISOs that are 650MB each. From Debian’s website :
To install Debian on a machine without an Internet connection, it's possible to use CD images (650 MB each) or DVD images (4.4 GB each). Download the first CD or DVD image file, write it using a CD/DVD recorder (or a USB stick on i386 and amd64 ports), and then reboot from that.
The first CD/DVD disk contains all the files necessary to install a standard Debian system. To avoid needless downloads, please do not download other CD or DVD image files unless you know that you need packages on them.
If you have any sort of sane Internet connection, you only need the first one, or just the netinst image. That's the way it's been for years, and I can't remember ever downloading images 2-N. They are there basically so that you can install the system even on a computer in the middle of the woods with no Internet connection at all.
The installation guide for jessie says that:
Much effort has been expended to ensure the most-used files are on the first CDs and DVDs, so that a basic desktop installation can be done with only the first DVD or - to a limited extent - even with only the first CD.
As CDs have a rather limited capacity by today's standards, not all graphical desktop environments are installable with only the first CD; for some desktop environments a CD installation requires either network connectivity during the installation to download the remaining files or additional CDs.
So even if you want something that's not included on the first disc, the installer will be happy to download it for you.
Those 8 CDs are equivalent to the first DVD. But as others have already said, you'd probably be better with the ~250MB "netinst" image. This can even be copied to a USB stick and booted directly.