Windows 7 automatically aligns SSD correctly, no worries there.
I'd go for the 850 EVO 250GB, works like a charm and its 3D TLC is more reliable than the usual planar TLC crap.
You can partition the SSD as you like, no worries. All SSDs come with built-in OP (Over Provisioning) space to ease wear levelling, in the case of the 250GB 850 EVO OP is 9.1% of the 256GB raw NAND capacity (i.e. ~23GB, that's why formatted capacity is only 233GB).
If you're paranoid about longevity, for peace of mind you can leave some space unpartitioned, and it will be automatically used as extra OP space by the SSD internal controller. Not really needed nowadays, unless you task the SSD extremely heavily writing dozens of GBs every day.
You'll love how fast the system runs from an SSD and will never look back.