I don't think there is any list on here that categorizes the difficulty of different dream powers. It wouldn't be very accurate because people can easily master some things that others would fail many times. For example, I can change light levels in my dreams easily, but many other people may find it very difficult. Summoning or finding a human dream character is really hard for me, but there are many other people who can do it easily.

It's more of a personal thing rather than a general thing. You could easily categorize it for yourself personally, but what one person might consider advanced another would call simplistic.