Windows 7 home is perfectly good for most home users.
There are few features that a home user might need.
If you have 4gb of ram, the 32 bit version is probably better since the os takes a bit less space.
But, with ram so cheap, 8gb and the 664 bit version is much better.
As to ram, your cpu is sensitive to supported ram. Go to a ram web site and enter your motherboard. You will get a list of supported ram kits.
All the major vendors are good.
Do not pay extra for fancy heat spreaders, they are useless and can impact some cpu coolers.