The script most important that I've missed

I see that you’re on the lesson screen and you already have the [Userscript] WaniKani Lesson Filter script installed, therefore you should have everything you need to rearrange your lessons. You don’t actually need to use the Reorder Ultimate script to do that.

The orange, blue, pink, and purple boxes mean: batch size, radical, kanji, vocab

So if you have 34 radical lessons and want to do 10, you’d put 10 in the first box, 10 in the second box, and hit ‘Filter’