Not to my knowledge.
It borders province 1793 (El Djouf), which is wasteland.
I'm not sure which it is, but it makes no difference in your case. If you can make Arguin your capital, you're good to go. If you're unwilling or unable to wait until it grows up into a city on its own, I suggest "losing" a war in which you give up Cape Verde; with Arguin as your only remaining province, it becomes your capital (and becomes a city).
Yes, that's how it works. Must have land connection to capital. No, it's not clear from the name it is given, sadly.