So I am debating on whether or not to use my one core or quad core pi as the nfs root for my pi cluster. I do not know much about nfs and am wondering if the amount of cores matter. I appreciate any input.
You do not need multiple cores. NFS transfers usually only use one CPU/core. You will have already reached your Ethernet connection's limit before you hit your CPU limit. It only matters when you heavily encrypt your transfers or when the CPU is already at 100%.
Your single-core pi is more than enough. Even a Pi Zero is way more than enough. But, it wouldn't hurt to use a Pi 2 if you are also running lots of services on it.