as for windows 7 it will add files to the SSD when you do updates , install a game on another drive etc.. so you want the biggest amount of space you can afford .
other than that the one i linked should be plenty for what you listed.
A 120GB SSD will have closer to 90GB after you format and overprovision it (use Samsung Magician software to OP once Windows is installed for Samsung drives).
I'm using 70GB on C-drive which is considered on the high end with NO games installed. As said, you'll install Windows but see the drive usage go up and at some point it stabilizes (Restore Points, Automatic Updates).
So I give you two choices, both Samsung 840 EVO's:
a) 120GB $90
b) 250GB $180
Now an SSD will do little for most games. I know, I've got many games on an SSD. It LOADS games roughly 1.5x to 3x faster which IMO is only worth considering for games with frequent in-game loads like jumping map points in Skyrim.
I think the 120GB might be a better idea and install the game to the hard drive but you can make that decision based on the above facts. It really comes down to money, is the slightly quicker loading worth it? For me, in Skyrim it was though I use a 2nd SSD for some games and an HDD for others.