It is not necessary to do all those lessons at once. They can stay there for months, if you are too busy to study new items right now.
When a kanji reaches guru status, all the vocabulary (purple background) words associated with it and any previously learnt guru’d kanji suddenly becomes available. I find it helpful to select those items for new lessons because it reinforces a freshly learnt kanji. Use the Reorder Ultimater script to re-order your lessons so that previous level’s vocabulary items appear first.
At level up time, not only will you get new vocabulary but you will also see some new radicals and kanji from the new level. That is why there is a sudden increase in lessons at level up time.