OmniCC is an addon that adds text to items/spells/abilities that are on cooldown to indicate when they'll be ready for use, like this:
Basically, OmniCC turns all standard analogue cooldown timers into digital ones.
No. OmniCC only adds text information to cooldown models. If you want that kind of information, then I suggest installing Inline Aura. It works great with OmniCC.
(Inline Aura working with OmniCC)
OmniCC works on anything that's visible and has a cooldown model.
(A cooldown model)
By default, OmniCC automatically adjusts its text size based on the size of the object it is displaying text for.
You should learn about OmniCC configuration menu.
On that case, then you should read this guide.