For what it’s worth, I’d strongly suggest trying to get into the habit of doing reviews daily rather than every other day if at all possible. My learning pace seems most efficient if I drive my number of reviews to zero at some point during the day every single day. I inevitably miss a day here and there when life intrudes, but WK (and any SRS) demands a regular cadence of reviews and implicitly expects them daily.
Think of lessons as the control knob for how many reviews you’ll have weeks or months from now. If you do 80 lessons in one day, you’re guaranteeing you’ll have 80 additional reviews added to your queue on multiple days in the future — it’s usually better to spread them out.
It’s okay to be more aggressive in the early levels, but beware that your review queue can grow extremely onerous in a few months based on the decisions you make today. Personally, I’d find it tiring and demotivating if I had more than 150 to 200 items or so to review on any given day.
Personally, I’m more interested in learning things well than I am in getting through the levels quickly. I can’t help but notice people getting to level 60 then immediately restarting to better learn things they’d already covered. Nothing wrong with that, but I’d rather take my time up front.
To each their own, of course, but what’s worked for me so far is daily reviews (getting down to zero reviews at some point during the day) and doing just enough lessons each day to keep around 100 items at the apprentice level.
My pace has slowed down a bit recently (around a two-week/level average now) but I rarely have more than 150 items or so to review thus far.
If (when) I start having more than a couple hundred items to review per day, I’ll stop doing lessons for a while and focus on burning more items. About 150 reviews/day is my efficiency threshold for staying motivated and not getting bogged down (in practice, it varies quite a bit: some days 80, others 240). Others may have a different threshold.
One final nuance: I distinguish between “purple” lessons (vocabulary) and “pink” lessons (kanji). I’m a lot more aggressive doing “purple” lessons where I’m learning vocabulary to hammer home the kanji I’ve already “guru’d”. But I almost never do more than five pink kanji on any given day (the only exceptions are characters I already know). To avoid paying for it later, I rarely do more than 15 purple vocabulary lessons on any given day, either.
After following this regimen for a little less than a year, I’m already comfortably reading much, even most, of the Japanese material I come across daily (admittedly, I didn’t start WK as an absolute beginner). It’s mostly just email for work and social media correspondence with family, but to get to this point in just a year was almost magically “efficient” to me.
Sorry for such a long reply, but to distill it down to one point: Is your “efficiency” goal seven-day level-ups or learning to read (and even write) Japanese as quickly as your brain and motivational energy levels can handle?