1. My understanding of robes (someone correct me if I'm wrong xD):
In Hogwarts, the robes are the cloaky things worn over the top of the rest of the uniform (the shirt, pants, tie, jumper etc). Dress robes are the same, but usually embellished somehow to make them more fancy.
2. There are a whole bunch!
Wiki actually has a nice list. Places like Tinworth (where Bill & Fleur live) and Godric's hollow are totally magic communities. On top of those are places like Dahliental & Chatoeil in France and Neroli in Italy that are MH "canon". Wizards could potentially live in any muggle city/town or out randomly in the country too, and I imagine that every big city would have some kind of wizarding area, even if it was just like Diagon Alley and mostly full of shops. Of course, you also have the option of just making up a little town for your family to be from if you'd prefer. Plenty of options

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3. I think another admin could answer this one better than me, so I'll leave it for now.
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~Savannah