120GB for OS, Office and major apps.
Basic 2TB HDD for games and storage.
As big as I can get for the least money!!
I personally would want just OS on one very small one (physically and... err... gigabytually) that could sit out the way somewhere, with Office and apps on a second one (say120GB) and games/storage on a massive 3 or 4TB one.
OS one makes any potential reinstalls nice and easy, along with not borking your other data if the drive fails.
I consider something like that, yes.
Whatever sounds like the best deal going, really. They'll get bigger and cheaper as time goes on, for sure, but there'll come a point when we're laughing at anyone still using "crappy old SSD tech" instead of Neural Gel Packs or whatever follows.