I would set system to 20GB depending on how many applications you install and also Windows Updates, Antivirus Definitions, Etc but I think 10GB is too small, you gotta think down the road a lil bit, it may be good for now but what about 6 months from now???
Applications, give it 15GB to 25Gb more than the total size of all your applications you have now.
Games, same way as applications...
Data, give it the most