I would say the one only rule is simply referring to tiles actually in the factory, I see nothing wrong with having an additional tile of the same type outside to be installed on a later turn.
This is corect.
INSIDE The factory, you can only have a single optimization and a single control (in the rooms on the right side of the factory).
If you want you can buy more of these tiles to store them next to your factory board instead of placing them into your factory.
It is an expensive tactic (just buying tiles so other players do not get them), but a valid one.