There are no rules in terms of how many you "should" be doing each day. For instance, someone could currently be doing 10/day for their language, because they just don't have a lot of time, and they don't want it to feel so overwhelming that they stop studying. They might even turn it down to 5/day at some point. So don't feel pressured to stick to some study schedule that isn't working for you! As long as you can maintain some sort of regular study habit, you'll keep moving towards your fluency goals.
There are a bunch of factors that will change how often you mark your cards as 'Incorrect' (different students, different languages, different studying styles, and different language levels, to name a few). And the number of cards you mark as 'Incorrect' will influence how many cards show up each day for review.