This page lists all the ranks that are available on MCAU, along with their region and home counts.
See here for donor information

Rank [0] is the basic rank all players start with.

Rank [1] shows that the player can build to a standard.

Rank [2] players have shown that they can surpass the building standard. This requires a lot of effort to achieve.

Rank [3] players are masters of the art of building and have created exceptional and, in some cases, extravagant creations. This is a rare achievement.

Your regions and homes will not be removed if you drop out of donor status back to a regular user. However, if you're over the limit you may have to remove some if you wish to create additional ones.

Staff have several ranks themselves. Their levels are monitored and maintained by the operations team.

[+]Alumni are former Staff Members that have stepped down from being staff. Their names are labelled in blue.

[J]Janitors are helpers and chat moderators. While technically not staff, they can kick and mute players.

[S]Staff are Staff Members. Enough said.

[S]Operators are also Staff Members, except they can make the server explode in fire and brimstone.