Sorry I don't know the exact wording on the "rule of 3"

Is it that nothing can be increased more than 3, or, only combat values?

If I have more than 3 opp. tokens can I use them all at once? The card says remove any number of tokens, and your increasing the die roll its self, not any combat values.

Thanks for the help.

Only combat values are governed by the Ro3. Opportunist doesn't affect those, so you can modify as much as you want.

Modifying the attack roll is different than modifying attack value, so you could use all 5 tokens on the card to make your attack hit.