Well, I think mostly we can only meet on 1 day, as I need to spend a night in Alor Setar as well (Wife's home). I will let you know when I have the final itinerary.
As for hidden places... hahaha... They are not really that "hidden", and they are all over the place. But if you're looking to cover most of the scene, I don't think it's possible as there are A LOT!!! I spent half day (10am-3pm) solely on the wall painting hunter on bicycle. I think maybe I can give you some suggestions, to let you "clear" your time on the weekdays, then maybe if we were to meet, we can settle on 1-2 spots to cover on that day.
If you don't mind, I will PM you my number, then we can discuss your itinerary in Whatapps before you get your group together. At least plan's ahead, and it can gives some ideas to those who are going to join you.