I dont have 400 watter, I use 1k but what I've been told. For 400w is for only a couple of plants( 2 or 3 maybe) & you can have them closer to the tops. As far as scrubber goes, you should be fine but there is always other stuff u can buy to help out like "ona". & for a humidifer goes you wont know until you start growing. Goto your local Hydro or even Homedepot & get temp. guage with a humidity monitor & that will let you if need one. No reason to waste money if you dont need to.