I usually do a partition for my OS, and then another partition for storage. This way if you do ever have to reformat you will have all your files on the other partition separate from the OS. The downside to this, is that if your hard drive ever fails...your stuck without your data, so thats where a backup drive comes into play.
when you initially install the OS on your hard drive, it gives you the option of creating partitions. In this case, you would create one that is for the OS, and another for storage. What OS are you planning on installing? I can possibly give you further instructions if you tell me the OS.
For me 200gb is not much to work with. If you could get another hd for storage and use that one for your os and programs I think that would be much better. If not then it would depend on what os and programs you will be installing and still have some headroom.