64bit Windows OS have been in use for over ten years. There's no reason to stick to 32bit when it's greatly inferior in so many aspects when used for gaming. As others have said, it's also possible to upgrade from a 32bit version of Windows to the comparable 64bit for free so there's no need to worry about cost. If you have a system that is capable of running FFXIV at a decent rate then it's likely to be 64bit compatible.