Glad to hear that you like the system and character creation.
Our next product will be a "Creature Manual" dedicated to a plethora of creatures and encounters of many different forms that will also contain information on methods of determining what a challenging encounter is.
Due to the size of the Core Rulebook and our preference to not mix creatures with the core rules we have chosen to keep them in two separate volumes.
We are concentrating all our efforts to completing the next supplement as soon as possible, but in the mean time you will have to be creative!
Hang on to your creations though! Soon you will be able to contribute them to the AO Community and allow others to use your creatures in their adventures.
Thanks for your support!
MSL