I used to look at number of apprentice items as a gauge, but recently I’ve just been doing X number of lessons per day. This keeps my workload nearly even each day (unless I’m doing particularly poorly during my reviews).
So for example, while there are kanji in my lessons, I do 10 kanji lessons and 10 vocabulary lessons each day, and then when I’m out of kanji, I just do 20 vocabulary lessons. I really like this pace because by the time I finish the vocabulary unlocked from the previous lesson, I’m guru’ing the new kanji, and unlock more vocabulary.
Here’s the link to the seanblue’s userscript for filtering lessons by type: