In V20, Celerity passively adds to Dexterity. We will be using this rule.
But, it only takes 1BP to activate all of your actions, instead of 1 per action. Any round in which Cel is being used actively for additional actions, the extra Dex does not apply.
Anything using !roll will apply your Celerity to your Dexterity automatically.
Celerity, once gained, can be increased beyond the first dot without a Tutor, even if out of clan. To get the first dot though, one still needs the vitae of one that possesses it.