|The default cluster size of 4k is good for most applications. With that cluster size partition size is not an issue. The reason to partition is to organize things on the hard drive.|
Look at the link below for ideas. You should know that you can only create 4 primary or 3 primary and 1 extended partition. The extended partition can have as many logical drives as available drive letters.
With a 500GB I would recommend 3 or 4 partitions. First one for OS and a few key programs. Next partition for the rest of your programs. The third and fourth can be for your personal files and music, movies, etc.
You should backup regularly but it is time consuming to backup an entire hard drive because SOME of the data has changed. Once you install programs you probably won't make many changes to that partition so you don't need to back it up very often. Conversely, your personal files may need to be backed up weekly or more. You get the idea?