I have looked through all of the rulebooks and cannot find anything about how many Class Deck cards that a Rebel character may use on a single Rebel Hero's turn. Is there a limit?

For example, if I have 4 cards that may exhaust using strain or other costs may I use all 4 of them on the same Hero activation? Is there a limit to the number of Class Deck cards that can be used per turn if the costs can be met?

There is no limit to the number of class cards a hero can use, as long as the timing to trigger the class card is followed and all costs are paid.

Keep in mind the "Once per timing instance" rule as well.

However, I do believe there is this little know rule:

If playing against Reiryc and he is playing the imperials, no rebel class cards may be played without prior written consent from Reiryc.

It's in the RRG (rules reference guide) but since I don't have the RRG with me, I can't reference the page number.