And lastly, any other times I shouldn't use them? I read they should be used only up till flap 3, correct?
Correct. This is because they are inhibited in the landing config. Thus if they are extended when the landing config is selected, they will auto-retract to meet the inhibition. When they do that, the aircraft nose will point at the fields below you to compensate for the sudden increase in lift. Descent rate will then increase significantly and potentially de-stabilise your approach.