Facebook rate limits are complicated. If I understand it correctly, available tokens are shared between all users authenticated by the same app.
It is possible to get available requests from the response headers, but this is not possible in the current Connector functionality.
Yes, they expire and needs to be refreshed. You will get an error message about this and the easiest way is just to launch the Connector, login/logout. This rarely happens to me because I restart Excel frequently and this makes SeoTools re-authenticate automatically.