Too long of an answer, saving thread space.
Upon level up to say level 14, I finish vocab from level 12 if it’s there, and I use “Reorder Ultimate 2” and lesson filter for that. (For some reason WK randomly gives me Level 13 lessons before I’ve done all my Level 12 vocab lessons. Maybe that’s due to me using scripts thus confusing their vanilla ordering.) For vocab only days, I may do 12-16 lessons. Then once previous level cleared, I do radicals of Level 14 (and the number of radicals is getting smaller once you progressed, so this step is easy, can be tacked with old vocab).
Then I start 12 lessons per day streak with with 4 kanji + 8 vocab combo using lesson filter only. Provided 36 kanji’s per level, it takes 9 days. Then while waiting for kanji to guru, I’ll keep doing the rest of vocab, 12-16 lessons.
Just count number of lessons per level, and divide by number of days you want for level up. It will work on average. Levels have uneven number of lessons, so forcing number of days per level means unequal load in future reviews.
This is “Reorder Ultimate 2” link:
[Userscript]: Reorder Ultimate 2 [newest]
It has a bad reputation because people are abusing it skipping vocab completely.
I thought I could get away without it, but I need it because of my self-imposed rule of clearing all previous level vocab.
I never aim to have zero in lessons queue. With Vanilla WK, the day after you completed new radicals and kanji lessons, you may have zero lessons available, thus breaking streak on WK Heatmap. So I prefer to have 100-150 lessons pending, as long as I know that they all from current level or one below.