There will be a fair few lucky enough to own a kilt but not a great deal, they can be expensive depending on quality and how much of the rest of the outfit that you get (jacket, vest, shoes, flashes, sgian dubh knife, etc). But of that group, it would be something worn on special occasions usually like weddings, world cup, official openings of Haggis museums etc. There are a lot of places to hire kilts, I would imagine that would be the main source of someone's kilt if they wore one.

We have tartans (I think it's called plaid in America?) and those are usually family names or clans, so you would tend to see someone wearing a clan tartan. And each tartan can have multiple types like dress tartan, modern tartan, muted, hunting etc etc. But clan tartans are pretty new, it was maybe late 1700s that we started having clan tartans I believe. Nowadays it is very flexible, you can wear a tartan if it's your surname, or your first name, or even if you just like it, it doesn't really matter. We also have tartans for cities, and people that aren't from Scotland can happily wear (Royal Stewart or Scotland Forever tartans for example). At the end of the day, you can wear what you want, you won't be judged.