I agree with your lists and I'm really lucky, plus I need someone who doesn't pressure me and is willing to accept other means of communication if necessary as I draw a lot. And tell their opinion (if I ask for it and have good reasons for it) as I've never had a guide/suggestions and need some criteria of comparison to know how things can be perceived from the outside.

Uhm, I'm a great client as for timing/ payment/ willing to change/ homework, but I still think I'm far away from actually being the ideal client: I'm difficult to handle and convince and I think I can be pretty frustrating. The heart is slower than the mind :/