We had a situation last night where all 4 [E] dice came up Righteous Success in a row. Now since only 4 yellow dice came with the set can a 5th [E] die be rolled or is 4 the limit?

Also if a character having 5 strength is 5 spots into a reckless stance can he only convert 4 blue dice to red? Due to the same dice limitation?

The number of dice is not a physical limitation.

If another die is needed, simple re-roll one of the dice of that type already used and any results generated to the results from the rest of the dice pool.