Are there any benefits to partitioning a single drive? Yes. Having the OS on one primary partition and My Documents on another primary partition protects your folders and files if the OS dies. But not if the HDD dies. Perform routine backups.
Should i put my OS on its own partition? I do that.
Using partitions for Organization on HD? Yes, see above
Partitioning now and then setting up RAID 1 later? Probably not, you need at least two HDDs for RAID.