You are best not to partition it. You want to have space to get updates later and programs.
Likely 50GB is a good estimate for the OS and non-gaming programs. Then average 20GB for each game as some games are right at this, some are nearly twice the size. You would get about 22.5 (counting the SSD as a 500GB since part of is lost from storage advertising BS). Granted you will fit a lot of older smaller games