for amount of space, i would go with most hard drive space you can get. meaning 1tb and up. the pc will take longer to start up, and initially open up applications but once they are open and running, they should be fine. larger games might be an issue going to say different levels or like, as new stuff is pulled form hard drive.
with that said, i love my SSD as OS drive, and then my larger HHD drives. but i opted for a 1tb SSD. so i have some play room, without constantly looking to see if i filled up the SSD. 512GB SSD might even work. it has taken some time just to get to 648gb on the 1 TB SSD i have now.