"What do you mean by target speed?"
I mean the speed autothrust will maintain if it is engaged.
"We have to be at 1 at S speed and at 2/3 at F speed? "
No there is no such requirement.
"What is the lowest speed the plane can fly without flaps? VLS?"
In any configuration the lowest speed you should go is Vls. In Conf0,1,2,3,Full, you can go down to Vls. The plane can go slower of course, but this is not ideal (Except in case of Gpws warning or windshear, when you can go below)
"Whats does the amber = mean?"
Those are the VFEnext marks, indicating the speed you must be below in order to increase flap config by 1 stage.