I can't answer specific questions, but I can tell you that most spies would be merchants travelling to and from cities. As with more modern times, information is best learned from what you'll randomly hear out on the street from average citizens. You can tell the general wealth and welfare of a city by how crowded a market is and the price of a general good (i.e. grain, regional foods, etc.) compared to what it was in the past and how much it is in relation to other places.

Nobility, on the other hand, is a completely different subject and not something that I understand and so I'm not going to speak on it. Hopefully somebody else will be able to provide you with a more thorough answer, but the thing to keep in mind is that things are rarely as they appear in movies. More often than not, it's boring and makes much more sense.

In the book "The Art Of War" by Sun Tzu, he talks about spies in a time different then ours in communication and the way spies where used around old Asia may be similar to Medieval Europe.

He talks about how moving big armies is time consuming and resource consuming so having foreknowledge of a place for any reason could help, there where different types of spies. Local spies, which would be citizens of an Kingdom you need info on, then Inward spies, Officials of your enemies giving you info, Converted spies, which is spies of your enemy giving you info, then lastly, doomed spies, which where spies sent from ones own kingdom to another to gather information, in Sun Tzu time and place this was very risky and likely you would never get info from a spy you send yourself to the enemy kingdom.

This is all from the Art of War which is from Old Asia, but it might be similar to how spies would have worked and been used in Europe, hope it helps.