Since every item has to go through 8 reviews, in the steady state the daily number of reviews will be 8 times the daily number of lessons.
If you learn 5 new items per day, then eventually you will face 40 reviews per day.
5 lessons per day → 40 reviews
10 lessons per day → 80 reviews
20 lessons per day → 160 reviews
50 lessons per day → 400 reviews
100 lessons per day → 800 reviews
So another way to approach this question is to ask yourself how many reviews you can handle on your worst day. Then divide that number by 8 to determine a sustainable number of lessons per day over the long haul.
This is just a first approximation.
It assumes that you always do exactly the same number of lessons every day, you always remember every item perfectly, you never fail a single review, you never take a break from WaniKani, and you never, ever fall behind in your daily reviews.
We’re talking perfectly elastic collisions on frictionless surfaces here.
In other words, allow some elbow room for reality.
You may think that 400 reviews a day sounds doable, but if you skip doing your reviews for just 5 days, you’ll face a backlog of 2000 reviews, which could be so overwhelming that you lose hope and quit.
The number of daily reviews will be much smaller at first, because the later review stages are still lying in wait for you, preparing to pounce on you six months from now, on a day when you are busy at your new job, moving into your new house, starting your new exercise plan, training your puppy, falling in love, or whatever else people do that they didn’t know they were going to be doing six months earlier.
Plan accordingly.