a) Buying bindings without going to the store is ok if you know you definitely fall within the size range for the binding. The "iffy" situation is, for example, when your boot size is just at the transition size for a binding size change. For example boots at size 9.5 and 10 are the max range for say a medium/large size and the minimum range for say a large/XL binding. Then things like boot footprint come into play.
b) In addition to bindings suggested, you may also wish to check out the Union and Flux binding websites. All bindings have a plus and minus in terms of weight, comfort of straps, how well the toe strap holds, responsiveness, do you prefer aluminum or plastic etc. I think more research on this by yourself, rather than just reading this opinion poll, is warranted.
c) White bindings. Anything white will get dirty-ish. But in my experience, playing in the snow helps give it a "wash" and it may darken after some time, but still be decently white. I would focus more on function than on binding color, but I can understand those who put a premium on style.
On a side note, I've never heard of anyone giving so much thought to cleaning their bindings to maintain their looks (Are u serious?? Its like giving your board a blowdry and topsheet wax job after riding. Surely just good airblaster work after riding will do. Its more important to maintain your hardware in terms of function i.e. tighten the binding screws, wax your board (base, not topsheet), tune ur edges, clean your goggle lens etc rather than be obssessed about how your binding looks).