I always did all lessons at once, getting big batches of 100+ reviews all the time. Then during Easter I only did the radical and Kanjis, leaving the vocab lessons for later. When I finally managed to sit down and do the over due vocab I had 600 lessons to do, and those never got passed guru, where I let them collect dust until they where forgotten.
Now I do only 10 vocab lessons per sitting, 3 times a day max. And if I do radicals or kanjis I don’t do vocab.
With this speed I get zero on lessons twice per level, and very few reviews per sitting. I also try do reviews as soon as they become available. So far it is working =)
If I ever feel overwhelmed I will do vocabs before radicals and kanji and thus get slower levels.