My vote is to keep the primary C: drive as small as possible, say about 4 times the space needed for the o/s. In round numbers 10GB maximum though I set mine at much less.
Then divide up the rest into 10 - 20 Gb chunks.
If C: is deliberately small it takes much less time to use Ghost or Drive Image to backup the O/S to somewhere else, and restore it when you sooner or later mess up the C: drive.
As well to start with a plan, but with Partition Magic you can change the partition numbers and sizes around later if you have to.