Q: What levels of OSX support Windows 7 32 bit?

I would like to install Windows 7 32 bit under Bootcamp on a Mid 2009 MacBook Pro 13 inch.  I am going to do a clean install of OSX.  I can see what levels of Bootcamp support Windows 7 32 bit and it will work with my MacBook.  The main concern is that I would like to reload OSX from scratch.  The MacBook is currently running Mavericks.  Can I do a clean install of Yosemite or El Capitan still run Windows 7 under Bootcamp?  I cannot find a listing of which versions of OSX are related to the various versions of OSX,  Are they not connected?  Lastly, how do I get the new version of OSX that I will run?  I am currently running on a MacBook White 2007 that is running Windows 7.  My son just got a new MacBook Pro, so I want to use his old MacBook Pro as my upgraded system.  thank you